Slade’s grounded up-special being able to slide off the stage is very stylish and a fun way to grab ledge. Occasionally you can hit your opponent out of a jump and convert into an edgeguard which is fun. Also occasionally your opponenet grabs the ledge first and you have to watch slade very stylishly fall into the blast zone. This doesn’t occur very often, but getting a conversion off of slide-off up-b also doesnt happen very often. I think it feels strange that the negative outcome is so much higher impact than the positive outcome. This option feels high risk and low reward.
My suggestion is to let slade wall-jump out of grounded (and only grounded) up-special. Now slade could intentionally not grab ledge to keep a weak, lingering disjoint near the wall and then wall jump to save himself. Realistically, this would still be weaker and less safe than going for invincible back-air from ledge (or maybe even ledge-special), but it would be a cool and unique option for the character.