I don't think it’s a conflict at all.

The invested time consistently into the things that were important to improve. If the art was good as-is (and it was), they didn’t waste time “perfecting” it further.

But as long as the gameplay itself still felt fuzzy or like there was friction, they spent time improving it up until their deadline. This was not a lack of project management, this was project management actually done well, for once.

In fact they accidentally optimized Super Mario 64 around its debug-mode performance, and shipped the game in that state, with debug symbols and everything. But they could get away with that because the game they shipped still landed in the performance budget they needed for the gameplay they were after.