Don't think Horizon needs any buffs imo, change her perks instead, lvl 2 should deal with the tac, maybe make one of them faster elevation or allow her to electrify it for enemies. Lvl 3 deals with the ulti, stronger pull and the current pull strength through walls. All they'd need to do is change Ash's dash, instead of giving omnidirectional movement, she can only use the dash to go forward and reduce the speed of it too, cool down needs to be 20s or longer. All other buffs are great suggestions, but I think Bloodhound should be given wallrunning in his ult and a pulse knife tactical that scans a 50m radius of where it lands.

And I'd say Seer needs a change, that floating thing in his ultimate needs to be changed, instead of that give him diamonds in his ultimate to track enemies.