One thing that served me well, I think, was ambition. Even before I went to college, when I was first falling in love with philosophy, my goal was to solve it. I wanted my worldview to make sense, dammit, and not be full of contradictions and incoherencies and "we don't ask that question" moments. Most of the philosophers regarded as great (Leibniz, Russell, Lewis, etc.) were grand systematizers who attempted to have an answer to everything, and were not satisfied with paradoxes/contradictions/incoherencies/articles-of-faith anywhere. Alas, no one so far has been able to succeed at this ambition, but nevertheless I think I learned so much more, and came to beliefs that are so much better, because of it.
Why? Well, one reason (though probably not the only reason) is that it helped me prioritize. It helped me move on from interesting-but-not-that-important puzzles and go for the Big Questions. And go straight for the throat instead of lollygagging.
The experience of trying to construct a coherent, non-contradictory complete worldview, only to encounter some new problem or puzzle that brings it crashing down, repeatedly is perhaps analogous to the experience of trying to construct a hypothesis about how celestial bodies move, or how optics works, or something, that can accurately predict all the data from all your experiments.
I’m curious about how one would know one has become better at philosophy? For other skills, our reference point is either an objective metric, or the regard of our colleagues. But for philosophy, there’s no metric, and it sounds like you’re saying that the regard of one’s colleagues is not a very useful signal either. After all, you’re claiming that studying philosophy made you no better at the subject, and seem to be characterizing your experience as typical.
Anyway, this seems like the key problem. How can you know how to improve unless you have a way to define improvement? And yet philosophy resists such a definition perhaps more than anything else. Except in the sense of “being familiar with more and more works that are deemed to be important works of philosophy.” That seems like a place to start.