It is a viable option, assuming the game isn't locking the exit like it does with some arenas.
There aren't that many unique things (like weapons or cores) to find in the game and they're often hidden in places where it's safe. Taking down multiple enemies means using a lot of ammo, especially without the firepower upgrades. A good tactic is to try and explore your surroundings before some enemies "wake up", so before completing an objective or approaching the marked exit. There's also quite a lot of checkpoints in the game, so you can go back if enemies spawned too early.
As for ammo, I had to buy it before several bigger fights later in the game, despite spending most energy on firepower upgrades. I was able to rely only on loot & crafting before that. Part of it is because you're encountering heavy enemies more often in the late stages, even those who were treated as bosses during the first encounters.