I also climbed to Masters using Tanks.
First, you need to know when to go which Tank. Which can solofrontline (Johanna, ETC, Garrosh, Malganis) and which can’t, which can counter dive and which can handle poke. Which is good against what comps (Anub against Mages, Artha against melees). Which is good with your comp or not (Dibbles, Anub, Mura enables dives, Jojo and Blaze are good at defense, sitting in the front so your backline can deal dmg).
After that, you need to look for enemy mistakes and protect your allies so you are focused and not them while they can deal their dmg. Distrupt key targets and abilities. Anchor camps (you deal low dmg to camps but you can zone an invading enemy out).
But if you play Tanks, you are at the hands your allies in a way. Since you can’t waveclear well enough, can’t do camp quickly, and you’re not supposed to chase, but who knows your team will follow up on your engages or not.
Tanking imo is the hardest role. So if you’re at yourreal skill lvl, you’ll have a hard time as them in low elos.
If you’re solofrontline, don’t dive. If you’re not, that’s your Bruiser’s job.
Tanking (imo being a melee in general) is about a back and forth playstyle. You go in, interrupt some abilities, draw aggro, and you go back to your team.
No need to babysit the enemy Tank or Bruiser 0-24, tho actually, focusing the Tank is a totally good chocie to make during a skirmish fight. You all can retreat after (if you all went low on resources (hp/mana/energy)) and go back forcing a 4v5.
I suggest you watch some Tank play from high ranked Streamers on from pro league.
I’m not a Streamer, nor a pro, but here is a good Tank match I did this season:
I was Mura against a Garrosh and my main job was basically just making him throw me and jumping back.