Second your unpopular opinion
I think if you can stragically place your slows, and use them well, then you will get a lot out of them.
I use my +20 Colen all the time in raids and wars. He obviously shines in rush tourney. If I had Azlar emblemed I would be using him instead. If I had C Azlar I would be a very happy boy.
Sumle also gets use in wars and events and is devastating when paired with Wilbur.
I use Jott in my red titan fights and blue mono raids, he has quite a versatile special.
I use LJ in difficult PVE levels and he has helped me to beat some bosses I was otherwise struggling with (although now with Mist joining me I may not need him as much)
I use Noor in my main Anti-Tell team, she is great for me. And no other better hero for PVE in my opinion.
C Quintus plays a very valuable role in my purple stack and when Grimble fires strategically Quintus turns into an average speed. Following C Rig and C Tibs his special is devastating
I have Justice who I regret maxing and who only ever comes out to play on 5* rush tourneys on a wing or flank
I just got Shadereave who I think may get a spot on my green titan team, and probably in my 2nd war team - TBC
I think the key with slows is that if you have a team of 5 slows you will die, every time. But if you team them strategically with faster heroes then you can get a lot out of them. And as a bonus its fun - more fun than just playing with the (generally) simpler specials of fast and very fast heroes