She has damage boost that is big enough to make it so her attacks that couldn't even get past someone's dbz
aura, could rip through it and land lethal blows afterward. Literally nosell to oneshot type boost.
Ecco's healing is good and quick, except he's being bombarded by dozens of attacks literally every second, sure he might avoid some, but he can't exactly avoid them all given they'd be coming from every direction so no matter where he'd dodge, he's getting hit by one. It isn't so quick as to outheal her attacks given it takes 5-10 seconds for him to heal, in fact she's fought people with even better "healing" (well less healing and more they Type 2+biomanip/blood that can recreate their lost body parts), than Ecco, and literally overwhelmed them with her DPS and danmaku.
mind you, Ecco's healing is only like
"
High-Low: The ability to regenerate severed fingers, toes, or ears, minor organ damage, and even potentially reattach lost limbs. For machines and vehicles, this would be regenerating some interior damage, along with some minor critically damaged or destroyed parts."
And Ecco himself is at the very bottom of that tier, he isn't in the "oh yeah he can reattach body bodys or regrow stuff" category, he isn't healing major organ damage, holes in him, etc. And it still takes him like 5-10 seconds to heal it off from his pov, while he's going to be constantly dealing with Fern's pressure at a much quicker rate.
Fern's stamina is good enough to where she can fire countless attacks for who knows how long, we legit never see her tire at any point when it comes to this so I can't say, people even get shocked that she can do so the way she does
Healing and stamina are not tied, he still has stamina.
This is also ignoring every one of her beams can explode with hefty AOE like here if she wants it too.
And this is just casually.