Pretty much, I think. Both of these games tend to throw metric craptons of stuff at the engine - way more mobs and on-screen splashes and stuff than you'd usually see in an RPGMaker game.
As a result, I suspect what you're seeing is the garbage collector going apeshit - it's only a ruby interpreter, which is solid enough for smaller things, but not so great at giant data structures.
At the end of the day, the line "bad console port" describes it fairly well -
you can do this sort of thing properly, but it requires some major planning and thought on how you're going to implement things.
For example, you can implement an ATB system with a bunch of threads and locks and madness, or you need to add in a micro-combat-round that advances timers and lets the right chars act at the right time.
Or you can do the "minion swarm" idea by just creating a bunch of minions with each their own AI, bogging down the system, or you render them but only have a very basic decision mechanism.
As a rule of thumb, if things slow down every step, someone is doing too complex AI and moving all NPCs on the map, even those far offscreen.
If it slows down every few steps, it's probably the garbage collector catching up on sifting through all the junk.
If it bogs down on a particular animation/scene, that scene wasn't optimized properly.
Of course, to do all these things properly you'd need major programming knowledge, which is why there's a ton of RPGMaker libraries floating around.
At the end of the day - a lot of one-man shops are a lot better at art than programming, which is good. At least bad programming can be solved by throwing a bigger computer at it.
