I’m stumped too. Gaderious is a great tank, but not if you want to be in diamond. The team would be better with Lianna, but then you don’t have a true tank. Also, Malosi isn’t great on defense, but he’s the best Holy you have. If I had to put something together…and I’m sure others would disagree. I’d do Athena - Malosi - Sabina - Tyr - Lianna.
I’d like to see what others think…I don’t feel great about my creation
I agree with @Chadmo, Malosi is poor on D as the odds of AI using his special well are slim to none. Rainbow D is a good goal, but not essential if the team works well. A 1-1-1-2 team can work just as well.
Based purely on who you have leveled now I would consider your emblemed Boril. Enemies take damage back which I believe would be increased damage if their D is dropped by Athena. I may be wrong in how that game mechanic works though.
Not sure Sabina is great in a flank either, she is a bit fragile. Wing may be best spot.
Good luck though, looks like you have great heroes coming up!