(1) What exactly? One-on-one units tend to last quite a while; but the right `push' or `shove' crushes even elite units like they're simply not there.
(2) Not our bug, essentially. It is a problem deep down in the core AI which is largely unaffected by what we can mod*
(3) Not going to happen; in fact if we are really pressed for unit slots we'd probably drop Imperial units altogether. As it is, Imperial reforms pretty much marks the death of the Republic as we know it in EB. No faction is remotely accurate in 14 AD as it is portrayed in EB: expansion, for one thing, is all wrong; and for many factions the depiction of internal structure and culture would be anachronistic (as these developed much more in the real world than is possible within the game) not to mention that units would be outdated, too.