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.