I think long term you probably need to just build some way of scaling core HP into the base of the core, something along the lines of +x* core health on <insert thing that is the identity of that core>. And completely make away with the flat +hp option on wave complete. Because currently you just pick HP early game to keep up with early stat checks. Then after that you get your core to 1.0s then you only pick hp after that. There really isn't much actual choice in that screen. So if the HP went away and just became a core mechanic of each core. Then it would probably help open up that design space to actually allow for some choices.
I think for me something more or less ideal would be if that screen always had "decrease cooldown". Then the other two would normally be 2 randomly selected reactions that you can add to your core (as in you get two randomly rolled ones, but you see what you get before you pick one), then a small chance for one of the 2 "reactions slots" to instead be a "upgrade core" option. That would lead to some actually interesting (and skill based) choices.
Random reaction in its current implementation is kind of problematic. Since 99% of the time any reaction you add that give shielding/healing/regen will just kill yourself faster against enemy poison reactions. So I personally never pick it, because any power it gives is so far outdone by how much it is 100% going to kill you later.
Also on the "improve x" option between waves. The increase power one needs to be rebalanced to something like +10% damage instead. Because when two options are multiplicative and one is additive. The latter will becomes useless by wave 2 normally. Adding +10% crit to a 120k power units is quite impactful, adding +10 damage is not. Same with the "sacrifice effect for power". That is never useful, +10 flat power is never stronger than whatever it ends up removing, and the gains are so small that something like picking gain random reaction -> sacrifice reaction, on repeat, won't ever be useful. Because it's just way too slow. So those two are basically "dead buttons" at this point.
I'm still not 100% sure on this. But it feels like fatigue damage is flat, rather than % of hp? Either way, fatigue starts way too soon and when you have 1k hp to your opponents 500k hp. It's not exactly fair. I've realized that some of the deaths I thought were to random poison ticks were actually just due to fatigue starting way faster than most builds could feasibly chew through 5m hp + shielding + healing + regen. And since it hits you super hard and basically doesn't seem to impact the opponent at all. It feels pretty unfair. Not like there's a counter to being one-tapped by fatigue when the fight has pretty much just started.



