Ugh, yes. I hauled a big one around for two weeks and it was a total letdown. My phone would charge maybe one and a half times before the bank was dead. It just became this heavy brick in the bottom of my bag that I had to find an outlet for anyway. Felt like more trouble than it was worth.
That "heavy brick" line really got me. I saw a tech review that said MANY of those large power banks have seriously overrated battery life. They might claim three full charges but actually deliver one and a half on a good day. The reviewer tested a bunch that lost power way faster if you used them while charging your phone. So you're basically carrying a paperweight that lies about its job. It makes the whole thing feel like a scam.