Consider a battle of 6 "balanced" orcs vs 6 light Infantry: only 33% chance for the orcs to win!
Ok, now add the dreaded assassin to both sides:
Assassin +8% group ambush: 37%
Assassin +40% group ambush: 40%
Assassin +64% group ambush: 46%
...so the poor green skins still get pelted.
Or how about a paladin in shiny armor added to both sides:
Paladin +4: 42%
Paladin +10: 45%
Paladin +19: 47%
...nope, even the best Palading preaching cannot turn them to the better either.
So lets see how 6 orcs fare against real strong units - after all, that is were ambush helps best. Let's pit both against 2 battle blessed griffins in a city with +15 wall:
6 orcs: 7% (with 61% survival chance for 1st first griffin)
6 lInf: 1% (with 83% survival chance for 1st griffin)
...the advantage is as meager as a nerfed orc.
Adding a level 6 assassin with 6*8%=48% group ambush against those griffins:
6 orcs + Assassin 48%: 98%
6 lInf + Assassin 48%: 95%
Or adding a level 6 paladin with +13 Leadership against those griffins:
6 orcs + Paladin(+13): 36%
6 lInf + Paladin(+13): 27%
So heroes mitigate that slight advantage again.
However you turn it, the orcs are no fearsome warriors after the rebalancing. For 100% more upkeep and 50% more initial cost as compared to light infantry, you get a unit that is clearly inferior, unless it seeks shelter in a damp swamp. Of course, the orcs are a bit better at plundering, but isn't this balanced by the loss of a movement point and the construction ability already, as compared to light infantry or light cavalry that gets good terrain bonuses? Note that the same obvservations about the ambush nerf roughly also applies to the nerfed wolf rider.
So the poor green skins are driven into their secluded swamp reserves by the newcomer assassin, which was (and properly still is) way too powerful. Now that sounds unfair somehow, doesn't it?
PS:
This tongue-in-cheek post is intended as food for though, as a ground for further discussion based on actual numbers. Note that an orc would actually need an impressive ambush value of 25% to reach a 50% success chance against light infantry. I found 25% ambush to balance out 2 meager strength points quite surprsing - did I get the numbers wrong? (Note that the value applies to groups of 6 orc vs 6 light Inf; while 16% ambush is enough for 50% success for 1 orc vs. 1 light Inf.)
I actually like the diversity introduced by non-10 stremgth 1-turners. For flavour, I would prefer the orc to be throw-away shock troops, that kill en masse, and that are also killed in masses. A blood bath unit. Say, how about strength 14, 14% ambush and just 1 hit point? Wouldn't that be fitting?