Out of the 4, Cassidy seemed the most viable.
Widow still good for the first 1-2 picks in the beginning of the match, but after the enemy noticed and picked a counter for her, it’s an immediate swap off widow moment.
Junkrat is still a good hero against shield, choke point, and narrow maps. His biggest advantage is he can kill without peeking. Therefore, he is usually in a safer position and still doing effective damage. His weakness is there’s a clear counter to him, same as widow, as long as the enemy switch counter to him, it’s junkrat swap time.
-with the DVA buff and the addition of Illari, I don’t think Pharah is viable beyond diamond anymore. Unlike with Junkrat and widow, who only need to swap when the enemy picked a specific counter to them. In most games, there is always at least one Pharah counter.
Maybe a pocket pharah is still better than a junkrat and widow, but a lone Pharah is definitely the weakest dps.