Being online only just for that still isn't worth not allowing many people across the globe to not be even able to play the game at all. There are many games that don't get many complaints about 'cheaters' like the Borderlands games, Remnant from the ashes or any other single player co op game you talk about.. We're far away from a future where most people across the globe have lag free and good enough internet. I'll quote a previous post of mine instead of reiterating what i said to another poster some hours ago...
I'm going to again point out the huge flaw with this game and that's the developer's lack of foresight of not going with dedicated servers. They could have at least helped mitigate some of the issues regarding latency. Having centralized locations would have gone a long way, versus being dependant on peer to peer. Especially since people playing over wifi connections. I hope they revisit this, given the success of the game, well prior to the inventory wipe glitch.