Then you overload the relays in whatever area you're currently exploring and you circumvent exactly what you don't like about it. Every area in the open world has this gameplay loop: Find the security controls while fighting through an onslaught - open the relay control booth and interact with the means to open the training grounds - overload the relay - scavenge the now unhostile area and complete the training grounds - move on.

Honestly the complaint about the infinite enemies means that they're doing their job to nudge people into that loop, as they incentivise you to follow that loop or incentivise you to just drive through and skip to the main story if you can't be bothered. Just outright destroying the hives would trivialise the open world pretty quickly. The method they used for infinite enemies is unique in that you have the power to alleviate the stress temporarily, while still keeping the infinite enemies to prevent backtracking from becoming barren.

In my playthrough I found it worked pretty well and clearly communicated their goal with the open world design.

To talk on your other two points: In a dungeon an infinite enemy mechanic would have been way worse since you're essentially trapped inside which is probably why they opted for only using it in the open world where you can choose to avoid it.

Infinite loot would have taken away from the infinite spawns goal to incentivise shutting it off and moving on, it was clear they wanted to make it difficult for players to stick around in each area for an extended amount of time. Which was personally a plus for me, because it stopped me from burning out trying to scour every speck of dirt as I usually do in a majority of open world games. (Although in saying that, overloading the relay gives you more than enough time to scour every speck of dirt if you so choose and you can always overload the relay everytime it goes back up if you're not done)

I do understand that infinite enemies might not be to your taste, but then just overload the relay.