My take on your defense, with what you have on short term would be:
Caedmon, BoldTusk, Li Xiu, Tiburtus, Triton/Sonya
Caedmon, Tiburtus, BoldTusk, Li Xiu, Sonya/Triton
I’m not a fan of your offensive options. You have variety of healers, which is good for challenges, wars and inc Tavern Brawl. I also like your focus on 3/4* rather than 5*s, it will make you progress faster in the game.
Personally I dont like tank healers, because unless their ult is really punishing they can be charged multiple times for little consequences. But, in your case BT is heavely emblemed and if life give you lemons, do a tequila shot and squeeze the lemons in your eyes. Or something like that.
Last advice for defense: the AI will ALWAYS use your heroes ult from left to right. So if the AI finds itself with all 5 heroes with 100% mana, the sequence for the ults will always be Triton, Kas, BT, Li Xiu, Sonya. Which means, that Sonya’s dispel will come in last (and it should come in first with your team synergie).
Edit: if you really want to fit Rigard in: you may want to go for
Caedmon, Rigard, Li Xiu, Tiburtus, Sonya
Li is a weak tank, but it should force a x3 purple stack that will help your Rigard and Tiburtus shine. The problem is that we are not using BT which is a shame. You can also use 2 healers, I dont like that as it’s much easier for an offense team to find spots where to spam gems for very little consequences.
But, a 2 healer team with Rigard could be:
Rigard, Caedmon, BT, Li Xiu, Triton
Rigard is on the far left instead of Triton, because I personally value more the Cleanse rather than the Heal boost buff. But that’s just me.
to me, swapping in Rigard for Triton is the more obvious choice. Kashhrek may be a more canonical tank than Boldtusk.
So, if it were one hero to swap, I would go Sonya - Boldtusk - Kashhrek - Rigard - Li Xiu
But, that is a pretty passive defense. Queen of Hearts is a nice flank. I would also aim to get Mist leveled and the replace Li Xiu with her.
Sonya - Queen of Hearts - Kashhrek - Rigard - Mist
If that is still too passive, look to swap in Little John for Kashhrek, moving QoH to tank, though she’s not an ideal tank, either.
Replace Kash with Cyprian, imo.
Leave BT as tank.