I'd argue that the 2 deadeye limit for Very Hard, and Nightmare 6 or no limit. (or only no limit for planned higher difficulty, depends). You should be punished for not being on top for things for not taking out Deadeyes one by one as they show up (time management). "Kill the pick-enemies before they cluster." If you're proactive, you look for them before they even lock-on to you; hence in reality the effective time to manage is greater.
If they were incredibly, unfairly oppressive, they would:
- Have No laser sight (look for glow eye, firey jetpack guy in open sky)
- Have no visual cue (just glance at the sky every 10 seconds)
- Have no Audio cue (aforementioned)
- And do half or more HP because every other game, enemy sniper = high damage
-# this is not a suggestion. In a game with strong visuals, and an emphasis on skill and attentiveness; this wouldn't be unfeasible for players to learn to manage.
In short: Deadeyes could be worse. People think Deadeye is oppressive (that's it's job), but you must glance occasionally at sky and take them out before instead of after they're a problem
-# "why can 6 Deadeyes lock onto me?"
-# "why are there 6 Deadeyes alive"
On the topic of portals, I was perplexed by it at first, but considering mob aggro is questionable as is; I can easily see 4 sets of portals being chained to absolutely trivialize hordes.
-# That is, of course a reason they'd alter portal mechanics if portals were changed to be less limited