I used to have a group of bros in my last gym. We'd shit chat, meaning, intervals were above a minute and a half, always, probably bordering two and a half on average.
We'd also help each other, meaning, on every series we'd get concentric failure.

And we all had great results.

Is this optimal for gains?

I'm investing high on a diet, both money and willpower, so I'd rather to be doing the very optimal training in the gym as well. Since I'm not being advised to reach failure, I'm starting to question the teachers there.