The flight ability totally preventing falling damage never made sense to me, and with no evidence that this was factored into the cost of the ability this is my "most overdue" change to the 2017 rules.
I hate to further the "thematic" argument but to echo RobEng and Cliffjumper the knockback/falling damage is taking place during an opponent's action, not during the active player's turn. I've seen plenty of examples in comic where a flying character hits the ground. Really hard hitters get up, those without damage reducers don't brush it off.

I'm really liking that KNOCKBACK is 100% optional, although I think I'd like to see Combat Reflexes recover the additional effect to OPTIONALLY take KNOCKBACK from attacks.
I agree with your sentiment, but I'd say they explained their reasoning. I do find it peculiar that aquatic terrain is where they decided to draw the line on "the cost is higher than the benefit" of tweaking the rules!

My thoughts on the "to do list" for (possible) tweaks:

Force Blast

Maybe add back the side effect of using Force Blast during attacks? The 2017 change made it a pretty dull power.

Earthbound/Neutralized

Most likely tweak would be that figures that lose abilities can be treated as not having those abilities for other game effects (to be carried). The loss of Willpower seemed weird to me, but I don't that they'd change their mind there.

Leap/Climb and Phasing/Teleport

My guess would be the addition of a passive effect (but most likely not involving CAPTURE, as in the old days.) I thought these were pretty good, but it is clear that with full-dial movement now a thing these powers aren't quite what they used to be.

Super Strength
Charge and Combat Reflexes

Along with Force Blast on the list, my guess is that some changes to KNOCKBACK are coming.

Mind Control

Another nerf? My only thoughts are that many players have been frustrated by the "vanilla" attack (and/or move), and that something will be changing here. The 2017 change was so radical that I can't help but think they will keep it in place and just add some more wording explicitly about how it works as a 'friendy'.

Battle Fury

Could we finally get the option to make ranged attacks by throwing objects? More likely if anything changes it will involve some corner case with some other PAC power (like Mind Control).

Pulse Wave and Quake

If there is any change here, my guess is that Quake will end up targeting all characters in the area of effect to make it more like Quake. I suppose they might consider reigning in Pulse Wave, but IMHO that would only happen if someone on the rules team just got curb-stomped by an opposing figure with Pulse Wave!

Outwit
What he said. I have no idea what they would change here, except that many folks have expressed outrage about being able to preemptively Outwit a power... which seems perfectly fine to me.

The attack part is still there. Its in the key phrase of
KNOCKBACK
When one or more opposing characters takes damage from this character's attack...

Ah, good point! It isn't as vanilla as I thought! I guess I don't know what they would change, unless it is tied with SuperStrength/Charge/Combat Reflexes changes.

I could see 1d6 halved for POWER knockback

Decreasing that power would be crazy, which is why they will absolutely do it.