OP said he had to replace one sooner or later.

I think BOTH are wrong, actually!

The opener is not intended to "lift" the door's weight.

The door's weight is supposed to be counterbalanced by the spring. It needs to be, otherwise you're stressing the opener, and more problematic, it's excessive force to open manually, and may crash down hard when you try to close it manually.

So, it sounds like he needs a stronger spring, if the guy tried to tighten it but couldn't hit the target offset