[3.P] We know core is broken, but what breaks it, when, and how?

[Xefas]

But...it all comes down to the players and the DM, while the rules are easy to break, it is up to the people involved in the game to make it fun, and core allows you to do that somewhat.

I would argue that a system that is so fundamentally broken that it requires effort just to keep it from breaking is a bad system. There are other systems that actually do function on their own, and the players and DM get to expend their effort enhancing the game from enjoyable to highly enjoyable, rather than expending their effort trying not to look at the gaping holes and scurrying cockroaches and forcing the system to work even a little.

Ironically, I don't find the whole "Casters trivialize everyone else" to really be one of the fundamental problems of D&D as a roleplaying game. The above paragraph doesn't take that into account even a little. D&D has other issues that don't get much attention on these boards.