As others have said this is really only an issue if you're playing on the hardest difficulty. I've had plenty of success playing melee focused or exclusively melee armies in campaign. I've found mass charges to be effective and flanking with infantry units not terribly difficult to pull off.

The issue is that your only judging impact by damage. Holding positions, occupying other troops, and allowing ranged units to fire unimpeded is impactful. While TWW isn't historical it is based partially off historic warfare. And historically infantry was for "tanking and tarpitting". Battle weren't won my massacring the enemy's front line of troops. They were won by putting that front line in an untenable position. This is reflected in the morale system.

In that sense I do think that flanking and rear attacks should be much more impactful. Formations of troops that are compromised should disintegrate very quickly.