I argued that high-speed units are necessary.

These are very different things: the need to simply increase speeds because "high-speed units are necessary," and increasing speeds only for flying units while reducing their physical stats. So, yes, this is one of the solutions, and it ultimately worked well, but that doesn't mean that any other solution to increase speeds (for example, returning to the original) would be good.

The process was as follows: I first played a lot of battles, feeling the concept of the mod with slow units, and only then did I gain a clear understanding of who and in what proportion the speeds should be increased so as not to break the refined gameplay.