The point is that Terradons are a skirmishing troop without the ability to actually skirmish, because they have a glaringly obvious hole in their core design. Which is lame...
"to you" seems like the generic response to most of this. You have these very firm, sweeping assumptions about what things should be without really taking into context of what they are or have been.
Terradons have existed this way for, and i mean this literally, ever. They've never had run and and shoot. They've always been a unit that shocks you with their unique thing, dropping rocks. This continues to carry that forward. The fact you don't like that archetype and feel really strongly it should be different doesn't actually make them an inherently flawed unit. It makes them a different unit than what you want them to be.
I could largely say the same thing for spellcasting.
Like, if the vibe isn't for you its not for you. but that would be like me complaining that marrio doesnt have enough guns and jumping on things is "boring."
Spellcasting for the entirety of AOS has been incremental buffs to things. They found out in 8th edition fantasy that really, really powerful spell casting was simple put, game breaking. So they don't do that and haven't done that literally since the game has come out. These spells are in line with what you should have been expecting the entire time. Also, we care about casting on +3 because, surprise, unbinding exists. I just don't feel like this context should be something that needs to be explained. A single slann also can't be at +3, you'd n eed two (assuming astro doesnt also give +1). The spell effects OTHER wizards, just like it has in our last 2 books.
I'm also not super upset a large reptilian cow has roughly the same hitting power to a generational combat super soldier with the spear of destiny. That more or less tracks to me.
Also, old summoning doesnt exist. So, not sure why i'm comparing anything to old summoning. No one gets summoning. Our old summoning also wasn't 100% tied to the slann /shrug. got points for spell casts from any wizard and from every wizard. Could summon off every node. Had literally 0 to do with the slann, altho it was obviously pretty good at getting you extra points.
In comparison to similar effects other armies get, its super, super good. Because like i stated, it "costs" nothing. No CP. No battle trait. No once per game. its just a free, once per turn roll you get to make. Thats very, very good. It's also not something "most armies" are getting. Theres a huge chunk of armies that haven't gotten a mechanic like this at all, especially ones that didn't already have something similar in 3.
I genuinely dont know how much aos you are actively playing, but if you are actively playing and enjoying aos, this is generally pretty good stuff. If you're not actively playing aos and are waiting for it to become whatever game you're imagining it should be, then ya. I'm not surprised you're disappointed honestly.
TLDR: 4.0 is a fine tuning of 3. If you didn't like 3, which it seems like you didnt, and the reasons you didn't like it aren't associated with rules minutia (which they are largely fixing) you're probably not going to like 4... especially before literally any of the army books come out. Which are, ya know, usually the thing that adds a decent amount of depth to any specific army.
Final edit, don't mean to really dig into you that hard, but i think people enjoying aos now have every right to be excited for what is looking like a more finely tuned version of the game they already enjoy.
And i say that as someone who played over 150 aos games in 2023 (gearing up to be the same this year), from casual games with friends to performing well at GTs. I'm excited for the new edition, and i hope other people are as well.