Disc 4 being a point of no return while the final boss is far more difficult than anything else up to that point is a huge problem. The final dungeon itself isn't. And there's always a better way of doing something. Calling it technological constraints is bullshit, generally.
1. I'd say about maybe most of the time the main technological problem is coders that don't have a damn clue what they're doing, so that can just be written off as plain old ineptitude.
2. If there actually is a technological constraint--and I mean this within reason. You're not going to try to do realistic 3D graphics on an NES because that IS a legit technological constraint. Likewise, you're not going to have perfectly humanlike AI because, while that might not actually be a technological issue, it's not something that anyone really knows how to do (and, for that matter, if it's a matter of technology or methodology)--within reason, like wanting to have a really grandiose sequence going on but running out of VRAM to do it, then you scale back somehow and make it work. If you DON'T scale it back and get something that doesn't run right, then... um... ineptitude, again.
3. Finally, if it really IS a huge problem and you can't scale the thing back and still get the desired effect, then you're going to have to axe it, find some really, really creative way of making it work, or do something else. If you absolutely CAN'T do this so you sort of force whatever it is you're trying to do, run into a technological constraint, and it ends up breaking as a result... INEPTITUDE!
Or, the short version: If you screw something up when making a game, it's probably your fault.