No.... Not again.... Why?

Bruiser Fizz will always be decently viable in the same sense that other bruisers such as irelia can get away by building only 2 attack items and full tank and still kill a squish solo within their stun 1 v 1. He is very very similiar to bruisers in the sense he has no range poke (ults do not count) and has above average mobility. It is not like an assassin who leaps in and gets resets, he goes in and is left in range for retaliation even if he were to E away. While other bruisers like irelia, jax, riven have stuns on basic parts of their kit, Fizz gets an E dodge instead and fiora's parry is similiar to fizz's e dodge. Because of hard delays in his kit, he has around the same actual kill times as a bruiser from start to finish (start including when you throw shark) on squish champions. Riot will have to rework triforce and bruisers/itemization in general if they don't want that to happen.

Or maybe they should just also balance him around being a bruiser, since he is closer to being one than he is an assassin. His mobility is substantially less than most assassins if they can get resets and longer average kill times and unlike every assassin in the game, he doesn't have a range poke on a basic ability. He is stuck in melee for longer with less ways out and no way to contribute or weaken via poke before going in. Look at Rengar, who is similiar to fizz in many ways with how he has to catch the prey from range with an ability and then dive in, while staying within retaliation range. How many times has rengar gone bruiser? All the damn time.