The strongest melee Fighter as of Patch 8 is Eldritch Knight. The problem is that most of the damage of a Fighter comes from Great Weapon Master, Sharpshooter or Tavern Brawler. Using a onehanded sword and shield greatly reduces the damage.
If you don't mind using a twohanded weapon, you could make a controlling Fighter with Sentinel, Polearm Master, Savage Attacker and one ASI. I'd prefer GWM for such a build over Savage Attacker, but if you want to avoid it, the other variant isn't much worse. Anyway, a polearm build does play differently from a pure GWM damage build.
You could make the Fighter with sword and board and use Phalar Aluve, to increase the other party members damage considerably. With Battlemaster you still have the means to control the enemy, with Eldritch Knight you can still use Booming Blade and have 4 attacks with ease, that's 40 less damage than with GWM but still ok.
BTW my main is an allround Eldritch Knight Fighter, she has GWM and Sharpshooter and is Dex based. Her main weapons are Phalar Aluve and the Ttanstring Bow. I like to be able to act at any distance. Shooting a bow is also not as annoying as throwing, for my taste. It plays a bit differently than a pure melee GWM build, but in the end it's GWM when in melee, so maybe not for you.
If you don't mind a ranged Fighter, Arcane Archer is insanely strong (in my party Astarion is one), wether you use 12 levels Fighter with a bow or make an 8 Fighter/4 Rogue Thief mix with hand crossbows. Of course such a Fighter does play quite differently than a GWM based build.
To the rest of your group, War domain Cleric and Arcane Trickster Rogue may not be that strong, but a pure Wizard can win many fights mostly alone, if specced in certain ways and long-resting a lot, so I would like to come to Gale's defense here.
To be honest, I cannot imagine Lae'zel without a twohander. Because my main occupies that role, Lae'zel is not in my party except for the creche (my party always consists of Shadowheart, Astarion and Gale, while only Astarion is allowed to multiclass).
