Few exercises are so noncontroversial as chin- and pullups. Medical professional, gym enthusiasts, calisthenic people, crossfitters, almost everyone seems to like them. 1 The only people honestly not liking them tend to be strong and jacked (I mean even fat people acknowledge that they are just too fat, so they only jokingly dislike them).
There are of course several factors at play here, the two most evident being one, that of course it's a lot harder to pull yourself up, if you weigh more than the average gym goer with additional weights, and two, most people only half-ass pullups and chinups and then of course it is easier because they are only doing half of the movement. Occasionally we may witness people with veiny bulging biceps moving tons of extra weight, but it is a rare sight and we often miss the opportunity to stop and take the clues, namely that it is all about bulging biceps and moving tons of weight. 2
Chins and pullups are good exercises, but they require some effort to make them work, because otherwise they are only frustrating, hurt and take more than they give, but well, it's not that hard and bad actually, once you find a good approach and I argue that thinking of them as an arm exercise is a good one.
Nomenclature and admissible technique
First let us discuss how I use all the terms here and what is proper technique, because apparently the names and the history and technique diverged a little bit.
A chinup is pulling yourself up at a bar with a supinated grip, until the bar touches your chest. No touching, no rep. Like in the bench or overhead press. The other end of the movement is a bit more flexible, as apparently some people have shoulder issues or what do I know, but you should acquire some good stretch in the muscles involved
A pullup is pulling yourself up at a bar with a pronated grip, until your chin is higher than the bar. It is very hard and awkward to get the bar to touch here, so it's not a requirement.
One might interject that this should have been called chinup, but at some point the words have become confused and now we have this situation and the necessity to explain it once more.
Finally, you can have different grips, depending on the equipment available, or use of rings and other implements. In general you can clarify by prefixing the grip or equipment used and then use chinup if touching is a requirement or pullup if only the chin needs to pass a certain height. The same goes for kipping, though one might argue that it might be more sensible to view it as its own version, like a cardio pullup, similar how there are cardio machines for rowing which of course are not the same as barbell rows.
Program it like a big lift
The common way to stay stuck in the gym is trying to get with a certain weight to say 8 - 12 reps for three sets and only then increasing the weight. The reliable way to increase one's 10RM is to increase one's 3RM or 5RM and it's no different here. It's no different with chin- and pullups. Add weight, increase the weight added over time. Not necessarily on every session during the week, but if you are stuck, adding weight helps getting unstuck.
On the other hand, if you want to accumulate volume, do it similar to the big lifts, meaning lots of sets, lots of initial RIR (or RPE in the range from @7 to @9). The obvious problem with chinups and pullups vs. squats is that with the former the minimal amount of weight you can use is your bodyweight and for a very long time (read: forever) your bodyweight will be the majority of the load. While a bodyweight chinup is something almost no one ever achieves, a bodyweight squat is something you can get most trainees to in a year, if not much shorter times. So even unloaded you are usually closer to 80% of your 1RM than say 60% of your 1RM, especially in the beginning. Which means you usually need to be even further away from failure to accumulate sufficient amounts of volume.
It's an arm exercise first
Chinups and pullups are often slotted as back exercises, but ootb they suck at back. Any proper horizontal row3 or deadlifts are better back builders.
It is the classical "weakest link in the chain" problem; your back is attached to the bar via your arms and your arms are connected via your hands, and due to proprioceptive feedback you will not be able to fully engage your back as long as your arms are not up to the task.
This also means that chinups are the better choice in the beginning, as your arms are in a more favorable position and you can manage the load better, which is also the reason why beginner programs usually advocate these.
Bodybuilders often just strap up on chins and pullups, but as a strength athlete I think it is more favorable to build the necessary strength in all of the positions.
Having established that we will slot it as arm exercise, let us now also treat it as such. Consequently we actively try to primarily use the arms and support with the back and not vice versa. In particular we reduce the systemic fatigue experienced from chins (otherwise known as "fuck up your back for the whole week"). The back involvement can and will rise with more strength and mastery of the movement, but I deem it smarter to start out this way.
With chins now being some kind low rep high weight curl, we can also incorporate it in our arm routine in a more nuanced way, e.g. sandwiched between curls or after doing some back exercises, having a lighter curl variant and then doing chinups. A new favorite of mine is doing hammer curls before doing chins, because then my arms are already warmed up, my shoulders are a bit more ready for the external rotation and the pump is just otherworldly.
Wide grip pullups are weird, start narrow
There is some strange fascination with wide grip pullups and in German we even have saying "breit greifen, breit werden", which roughly translates to "grip widely, grow wide", and is, of course, as wrong as you can be while being right. In view of the ROM discussion, for most people wide grip pullups are the inferior movement and also usually pretty awkward. It's much more sensible to start with a narrower grip and then slowly build the positional strength to actually be able to have a good ROM and a smooth movement on the wide grips. A good grip is your press or clean grip, because it obviously allows you to get a bar to your chest or shoulders, so the only thing holding your back then is strength, but not anatomy.
I suspect in the calisthenics world one would call wide grip pullups a progression from pullups, as in the absence of weight, you move to more and more awkward positions to make exercises harder. In this sense we can already think of pullups as progression from chinups and program them accordingly.
tl;dr Chinups are a powerlift for the biceps
Once we can attach enough weight to have room to play around, we can just see chinups as a powerlift for the biceps. Keeping the awkwardness of the high minimal load in mind, programming them then accordingly as a big lift seems to work out much better than slotting them as some back assistance exercise.
By focusing the biceps over the back, we shift most of the fatigue over from the very central and systemic back over to the very localized biceps and maybe forearms. This makes it easier to program, because the reduced systemic fatigue means less interference with other training slots to worry about and overall the recovery of your arms is rather easy to gauge, simplifying questions of progression and volume allocation.