hmmm, I like: Alby-Boldtusk-Cyrpian-Wu/Gretel-Grimm
It’s a little beefy on the left side and punishing (but weak) on the right side but I think it balances defensive heroes and offensive heroes and gets a nice rainbow. Boldtusk provides some good cover for Alby and if they wipe out the right side, maybe Alby resrurrects them and they make the attacker pay.
What do you need the defense for? What’s your objective? Platinum, diamond? It should be diamond… Well, whatever it is, don’t give to much thought to defense. Your current roster won’t be able to keep you in diamond, no matter what formula you choose. But if you play your cards right on offense, you could open your chests in diamond arena, which is the point of raiding. You got some strong reds there… They might help with that. Soon as Wilbur and Colen get to 4/70, you’ll have an amazing offensive red trio BT / Wilbur / Colen. Take them to 4/70 and go hunting for green tanks! For successful raiding, think maxing at least three 4* of each color…
You have some pretty solid heroes. I would try Alby, Flex spot, Cyprian, Bold Tusk, flex spot. I use the flex spots for at least a week and see what happens to your cup count. Sometimes seemingly strange arrangements produce the best defense, and rainbow doesn’t always sustain more cups. But I try to avoid placing two like elements side by side. As far as future plans I have had some trouble with emblemed Hu Tao tanks, but I still like Cyprian better. Good luck with your team!