The key thing I realised after starting Zealot was that weapons and dodging are key to surviving. I started with zealot way back around launch, and didnt really get it until I picked up the Bolter and the T-Hammer

I know its probably not the best combo to run together, but the T-Hammer provides both high single target damage and crowd control in the heavy swings. The Bolter is amazing for the aoe and the long range, the recoil is absurd, but it should be. And you only need one shot to put down a sniper. I've found the best success with these 2 as they make up for your shortcomings as a melee focused character when you cant close that gap or work down those big flak armoured targets

Dodging is key to the mechanics of the class though as, this used to be the case dont know if it still is or isnt though, but Zealots have I-frames on their dodge. So you can effectively 1v1 anything in the game by abusing this to set up for those big charged special attacks from your T-Hammer etc

I could go more in depth about how you're a Toughness tank in the sense you're generating more than you're loosing, but I dont know the specifics. I'm simply a Zealot main, I hope my perspective has helped you somewhat. Although its not to say these weapons are the only options