I suppose we'll have to agree to disagree here.
-Before Sheen, he can't take a respectable burst out of someone to make his W DoT very useful (unless they go in a sustained fight while he has his W on or sit under his E, and even then without the extra oomph from Sheen, it's not that scary.
-Sitting under Fizz pole is what he wants you to do. If you must do this, at least have an appreciable amount of MR to negate the burst he gets from it. Friendly reminder that without his E, he has next to no escape and is so squishy that you'll likely destroy him in a straight up fight if you have any appreciable tank stats.
-Q is a dash, sure, but it's a targeted enemy-only dash much like Irelia. Note where he's likely to take his path and play around it (e.g. he jumps in with E, out with Q so make the direction he has to Q a bad one)
-Flask, as many have pointed out, doesn't negate his mana costs in laning terribly much. It still takes half to a third of his mana early game in order to do a full combo sans ult. The only way he gets "enough mana for it not to be an issue" is by buying mana (Frozen Heart, Sheen) which still leaves him without pushing power unless he uses his most expensive skill and also his escape: E.
-Play passive and freeze towards yourself. Nothing more irritating than this as Fizz because his melee means he has to recklessly endanger himself to grab farm that may be stuck under your turret if you've frozen far enough back. Plus, as great as his E is for an escape, it's not the full top-lane's worth of escape if your jungler has an iota of patience for him to overextend for that farm.
There's quite a bit you can do against Bruiser Fizz if you look for the openings. Again: he's strong, but not OP, especially with the new Juggernaut items that have made his mobility and some of his burst a moot point. Surprisingly one of the biggest counters I've faced is one of the most simple: Volibear. His W has a massive burst that absolutely destroys Fizz, he can build health and Juggernaut items to tank up and get damage at the same time, has the powerful slow on E and Q flip to catch Fizz before/after he poles and his passive means he defacto wins any all-in trade so long as it's up and Fizz didn't get a Morello (which why would you on Bruiser Fizz?).
Hope this helps you deal with the Trollfish in the mean time. I'm just waiting on the Juggernaut items to be less broken before I can do much again.