Most will probably say to stand pat. Telluria is still your best tank even with the latest nerf.
That being said…I just changed mine up just for the hell of it. I’m resting comfortably in diamond so I thought I would use some heroes that I LIKE using over the ones I was using just because everyone else was using them. I had previously been going with Misandra^20, GM^20, Telly^20, Drake^19 and Seshat^20. For the past couple of days I’ve been going with Drake^20, Ariel, Brynhild^20 (!!!), GM^20 and Killhare. Frankly I’m not seeing much of a difference in being raided. Just got bored with the new normal (or my version of it). So I say yeah, mix it up!
I like your idea about building around a Frigg tank. But I’d also be intrigued in Alfrike. I know the Very Slow mana is painful, but damn…she could be fun. If you decide to go that route you could swap in Kingston for your nature hero if intending to stay rainbow. Whatever you do, have fun with it. Raid defense isn’t the end all and be all of this game. Just a part of it.