The game heavily favors quantity over quality, and strengthening units makes them easier to hit (although I'm not sure how much of a factor evasion v power is). The randomness of battles (while faster) doesn't exactly help.
If the enemy goes first and focuses on a few of your best units, then your basically entering the battle with a handicap, since if a unit is defeated before they act that turn, they don't get to do so.
Personally, games where the only way to strengthen yourself is to increase your body to stupid proportions are not my cup of tea.