If my gym sessions are 300+ minutes per week, I end up too tired to increase the weight and I get weaker, it's counter productive.

180 minutes per week feels good but is pretty easy if it's 30 mins 6 times per week (or 60 mins 3 times per week). But that's where the effort-level really comes into it, how long are you resting between sets, etc.

So 150-300 minutes per week feels right but it depends on many factors. Elite athletes are genetic freaks, etc.