My upper body has come a long way on rings and my legs have done nothing, is bodyweight leg training actually a thing?

There is a real progression and you have identified the gap correctly. The principle that fills it is use one leg, and change the leverage - because you cannot add plates, so you have to make the same bodyweight harder.

The ladder, roughly:

1. Split squat, both feet on the floor, rear foot for balance only. Immediately harder than a two-leg squat because one leg is doing most of the work.
2. Rear foot elevated split squat. Back foot on a chair or a bench. This is the single most valuable movement on the list and most people can spend months here productively.
3. Step-ups to a high box, slow, no pushing off the bottom foot.
4. Assisted pistol, holding a doorframe, or to a chair you touch and stand up from. This is the missing rung you could not find. Lower the chair over time.
5. Full pistol.

And separately, because it is a different muscle group entirely: hamstring work. Nordic curl progressions, or single-leg hip hinges. Squat patterns barely touch the back of the leg, which is a large part of why bodyweight leg training gets a bad reputation.

If fifty squats are easy, you belong at step two, not step one. Elevate the rear foot tomorrow and you will find the difficulty immediately.

The diagnostic you are already using without naming it: if you can do fifty of something, it is not strength work.

Strength adaptation wants a load you can move for a low number of hard repetitions. Somewhere in the region of five to twelve reps where the last two or three are genuinely difficult. Above about twenty you have moved into endurance, and that is a real quality but it is not the one you are trying to change.

So the job is to find a variation where eight is hard. That is the whole selection criterion, and it applies at every stage.

Ways to make a leg movement harder without weights, in rough order of usefulness:

• Fewer limbs. One leg instead of two. The biggest single jump available.
• More range. Elevate the front foot in a split squat, or the whole body in a step-up.
• Slower. A five second lowering phase changes a movement completely.
• Pauses. Three seconds at the bottom removes any bounce and exposes the position.
• Less leverage. Moving the load further from the joint.

Combine two of those and almost anything becomes hard for eight. A rear-foot-elevated split squat with a three second lower and a pause at the bottom is a serious exercise for most people, and it needs a chair.

The honest limits, since you asked directly and deserve a straight answer.

Bodyweight can build genuinely strong legs to a point. Single-leg work with good range, controlled tempo and real progression will take an untrained person a long way, and further than most people assume.

It runs out earlier for legs than for upper body, and this is not your imagination. Your legs already carry your bodyweight all day, so the starting resistance relative to their capacity is low. Meanwhile a pull-up is a large fraction of your maximum from day one, which is why your upper body has moved.

Above a certain level you need external load for continued strength progress, particularly for the hamstrings and for anything resembling maximal strength. That point is a long way past where you are now.

What I would do in your position: work the ladder above for six months and reassess. You will get a great deal out of it, and by then you will know whether you want to add load.

And if you do, the cheap version is not a barbell. A backpack with weight in it, or a single heavy object held at the chest, covers most of the gap for a long time and costs almost nothing. That is a legitimate continuation rather than an admission that this did not work.