Full stop right here. If this is the tank you have the most fun with then it’s the tank you should play. All tank specs can get KSM, even in pug environments.
Since you’ll have a dedicated healer most of the time the two of you should just make your own groups. It’ll be easier and no worries about whether you’ll be invited or not.
I duo with a dedicated BDK and we pug our dps. We’ve been climbing the keys at a slower pace (I switched my healer main 5 weeks ago and we only only play together about 10-15 hours a week) and should be getting KSM in a few weeks.
Don’t fall victim to the FotM hype. Playing what you really enjoy will make the journey much more fun.