No, not really no, McCassidy was never really a good counter to a good Tracer but now its even worse, luckily she was heavily nerfed with him so basically it comes down to hitting her and not really relying on the Nade cuz it wont really work more than half the time, (wich is not easy at all considering her hitbox and ridiculous movement)
No kidding, the best tool Cassidy has against a Tracer now is his roll that allows him to survive a Pulse Bomb if hes at full health and time it well but he needs healers to be on top of him cuz he will be super low.
Cassidy is just weak in general though, specially to dive or long ranged characters, so i think hes gonna need some help, alot of nerfs to dive (and Sojourn) or a few buffs to him would do the trick.
I think something like this would make Cass alot more interesting: