GPU code performance != CPU code performance. You can have a visually trivial game (Dwarf Fortress pre-makeover) that will grind your CPU to a halt because of all the simulations it has to process. You can also have a visually complex game that will run fine because the rendering will be properly optimized to reduce drawcalls etc but as the number of units grows, it will push your CPU to the limit.

I tell people Dwarf Fortress is a cpu stress test tool, not a game.

The NES isn’t spinning up objects for every bullet on the screen or a million other ways a novice developer can blow up a GC.

No this doesn't look like NES graphics at all. This is more like the SNES era.