A long review merits a long response:
I mostly agree with your cover reviews.
Speaking of tape on comic bags, I tear regular tape all the time too, so I use Scotch Matte Finish Removable Tape. Maybe that's what you mean by matte tape. It doesn't stick perfectly, but that's better than tearing.
Middleton cover: I agree, the logo looks great and well-balanced in the top right corner and I would have chosen that one too. Your point about Cass's appearance is well taken. I had thought she even looked 0% Asian here, unlike her typical portrayals. But the nearly jet-back hair color he gave her could suggest that part of her heritage.
Main cover: At least it's not a bait and switch - it fairly represents the interior art, such as it is. I bought it despite that
. (More on that when I write something about #1.)
Inhyuk Lee connecting - I bought these too. I just liked the idea of it. The connecting elements are subtle and unlike most connecting covers, these two could easily stand alone.
Amano Yoshitaka - I don't mentally connect with this one.
Rian Gonzales - I love it except for the way Babs was drawn (more on that later, too). I didn't realize the plushy was Superboy.
Dan Hipp - it's okay. I'm not a fan of Teen Titans Go!. It's a bit odd the way Cass's cape maybe does, or maybe does not, become the Bat ears. I keep missing, then seeing, Batman.
Dan Mora - I like it. You're right, the focus is Barbara, and even Nightwing and Bruce are bigger than Steph and Cass which makes no sense for this series. Took me a bit to realize that all of the yellow is the inside of Barbara's cape. I do like the brooding Batman, though he doesn't belong here, but could do without Nightwing.
Kendrick Lim - They are both good, but ultimately disappointing. The logo interferes too much with the unmasked variant, and I don't love the anime faces here. The lighting on the unmasked faces seems so flat, compared to the highly reflective costume surfaces. As if they are wearing matte face power. I think the masked Steph is more successful, but I don't like the battle damage on that one. I'd never be entirely happy with either cover.
Babs Tarr - a fun homage, and you have good logic for choosing it.
Alex Garner - agree that the trade dress is a bad distraction and the minimal dress is much better. I do disagree with you a little though. I see how Barbara could be considered the focus, but she's a kind of apparition. Steph is foreground and pretty large, and I think the treatment of her cape is especially cool. Arguably there is no central focus to this cover - all of the Batgirls are off-center and that must be deliberate. The minimal version is expensive and the trade is imbalanced, otherwise I might have bought it.
Will Jack - The coloring is all over the map. It just doesn't look a Steph that has ever existed. The better version is the taller image, which is ruined by the logo, while I think the minimal dress version is spoiled by the close crop which eliminates too much of the full drawing. But some people might be more taken by that version. Overall the cover is going for the certain kind of attention that many retailer exclusives get. It is interesting that this is the only solo cover for any of the Batgirls. I do like the little batarang, the kind Steph used during her Batgirl run.
And yeah, just what is the deal with Steph's missing thigh belt?! I hadn't noticed that yet, and went back to check. It's clearly visible in all of the earliest post-Spoiler appearances, like Urban Legends #5 (Soon cover, Boo interior), Robin #5 (drawn by our man Jorge Corona himself!), Batman #112 (Jimenez), Joker #7 (March) - but it initially disappears in Batman #115, which is part one of the Corona-drawn backup.
There is a belt on the masked Inhyuk Lee variant - on the wrong leg.
For the most part, looking ahead at future variant covers, it's gone. But there may be a hint of something on the Kim Jacinto variant for #3.
Corona, or someone, may have drawn a new reference version, and that one is likely to get adopted across the board.
The belt has been a distinct feature for Steph for many decades, whether as Spoiler or Batgirl (though not Robin). This is clearly an emergency situation!