Hiya!
How is this escalating the power level? An unarmoured or light-armoured Fighter typically has a worse AC than a Fighter wearing heavy armour.
That's a change too far. We expect Fighters to fight so penalties for doing just that are in the land of Not Fun.
For the first paragraph: The escalation I was referring to was adding more bonuses to the AC. I see this as a step, even a small one, towards the classic 3.x "1-Up'manship" that the classes, feats and spells. I'm one of those DM's that has found that saying "No, unless..." is FAR superior to "Yes, but..." as is touted so loudly by many.
Rather than "add stuff to balance/encourage" I would look towards trying to figure out WHY this would be needed. It is usually easier to fix/change the source. If the AC's of lightly armoured fighters isn't enough then maybe it's because critters have too many bonuses? Maybe lower monster To Hit bonuses in stead. Or, what I suggested...
The second paragraph: One man's "not fun" is another ones "more fun". To me and my group "fun" is in the playing, not in the mechanical bonuses, per se. Don't get me wrong, it's cool to have a Fighter that has +7 to hit and +5, it's just not an overriding factor to determine "fun". Likewise, if another warrior type in the group doesn't have such things it's not the end of the world...as long as it's not the same "concept" as the Fighter (e.g., "big strong 2-handed warrior" A and "big strong 2-handed barbarian" B; if A or B is much superior to the other, then things get a little less 'fun' for the lesser PC....at least until he/she finds a different 'niche' to be roleplayed in").
In the OP, I can see the changes working. They don't seem like they would REALLY mess things up immediately. But then again, the OP didn't mention if the DM was allowing Feats, Multiclassing and all manner of other OPTIONAL stuff from other published books. If any of those are 'in use', then I foresee tears and sorrow ultimately resulting in "Naaa...lets go back to the old way...". But I don't know the OP's Players; maybe it will be fine. Different groups are different
Bottom line: I've always found it better to err on the side of "No" or "give less" as a DM simply because its MUCH easier to open a new session with "Ok, everyone can now add an extra 1,000xp because last session showed my new method of XP calculation is a bit too low"...than it is to open with... "Ok, everyone subtract 1,000xp because last session showed my new method of XP calculation is a bit too generous". Same goes for giving money, magic items, and bonuses to classes/spells/abilities.
^_^
Paul L. Ming