I know that there's some debate over whether or not Tabitha and Isabella are too good, but I honestly don't think they are. Granted, anything Tabitha puts herself into is really annoying to kill, but what she's in is the only thing she boosts. To build her CO zone she has to deal 30 damage personally, which can take some time. Her power is insane, but she'll be lucky if she can pull it off even once in a match considering that attaching her to a unit is akin to painting a big target on herself. Meanwhile, Isabella's CO zone is relatively small and her boost is also rather minor (though still useful, of course). If she pulls off her power she can really do some damage, yeah, but again, it's very possible to stop her before she does so. Even mediocre COs like Forcythe can get into her zone and take out the unit she's in unless the map has a lot of choke points or something (but honestly, I fear Gage more than Isabella in situations like that... Higher attack boost and larger CO zone make it so that it doesn't matter if his CO power isn't as good... heck, he doesn't even have to use it to be problem, Isabella meanwhile needs her power in order to be at her best).
That said, I think that tier list is off... I know for a fact Greyfield is at least mid-tier because his power includes resupplying building materials to units, which is amazingly useful once you learn the uses in temporary buildings (and having a single Carrier be able to build 8 Seaplanes is just plain crazy).
Waylon? Come on, at least agree he's better than Will (2 attack stars in a small CO zone that only benefits ground direct-combat units... whee...). Put him in a Fighter and you pretty much own the sky. Plus, maybe it's just me, but I personally find air units to be pretty fragile, so Waylon's defense boost really helps at times.
Tabitha doesn't need to worry about losing her unit. And if she did, she can just put herself in another and she's back to instant killing. Yeah. That's why she gets top tier. Let me check her boosts, I believe they total 160% ATK and DEF....oh, that's right. There's also the veteran boost, I forgot about that. So that's 180% ATK and DEF. Besides 55% on Roads/60% on Plains/65% on Cities/70% on Forests/75% on Mountains becoming guaranteed instant kills, Tabby's unit just plain refuses to die as well. 180% defense? Brenner doesn't even have that much defense on an individual unit, and, well, see my post from earlier. Oh. The Tank VS Anti-Tank matchup? Tabby in the Tank gets a severe advantage, at 54% (30% * 9/5) damage dealt, 41% (75% * 5/9) full health damage taken and that will get cut in HALF, if not reduced by 3/5 to 16%. It's ridiculous.
Hmm, maybe you're underestimating the infantry wall in general. The whole basis of that is to have the Infantry take attacks for your other units. What's it matter that they die, they're just computer bits that will be deleted anyway and so long as they stop your artillery from being hit so that they shower the enemy force with shells? So much for
Videogame Caring Potential. (Yeah, I'm aware that they cost 1500G each in Days of Ruin....but that was done in the theory that there's fewer of them in the mid and late game to stop the tanks. The problem is, you need them to capture cities to have the money for the units that can even handle the heavy combat duty in the first place.)
.....wait. Actually, 2 spaces isn't small for CO Zones by standards. Come to think of it, Brenner has the 3 space CO Zone.
Oh, Gage and Isabella have the same CO Zone. 2 spaces.
Greyfield's benefits for the Carriers aren't much. For 30000G, the Carriers are seriously underpowered. 8 Seaplanes, though not quite costing 176000G accounting for interest (you do have to pay that much still, just you can spend it gradually), is implausible when your navy is deep-sixed and your Carrier goes straight to the bottom of the brimy blue. Temporary buildings, you need air or sea units to even make use of them. That's out.
Waylon......maybe because air units are so expensive compared to land units if they try to be good. Choppers...I'm not fond of their lack of power against AA ordinance, they're virtually one-shot units, especially now that the AAs are less expensive in the (failed) attempts to make infantry spam a joke. Bombers are expensive and so are Fighters.