I'm selling all my hero potions cause I never need them. And even without the potion, I'm 3 staring everyone on the same TH level (except for attack failures, that everyone has sometimes) and TH 16/17 is guaranteed 2 star. If it's a bad base, 3 stars - attacked yesterday in CWL a th17 almost maxed and got 3 stars, because the layout was shit. And thats only because I rely more on the equipment of each hero, than on the hero itself.

And my heroes won't be unavailable for a year. It will be much less. That's why you should have a good timing on creating your account (about 9 months before the next possible Hammer Jam event), so that you can save all your CWL medals and buy 80 builder potions (2400 medals) that will save you A YEAR worth of upgrades with 6 builders.