Credit grinding is only possible on high level missions, which are easier done with the unbalanced weapons. Even then on average you will extract with 5-10 credits per mission, which makes the 1000 point buy-in take ~150 missions to complete, ranging from 25-40min per mission.

So you estimate someone playing an average of 30min per mission * 150 missions = 75hrs of play time (if you’re lucky to survive and extract each mission that is).

Or someone can pay $10 and instantly have access to those clearly over powered weapons.

This is by definition a setup of micro transactions, which is weighted to put players who don’t no life the game to feel like they have to keep buying credits to get usable gear.