I guess that, at minimum when going into raid tourneys, everyone would need (at both 2 * and 3 * troop levels) 2 maxed troops in 2 colours and 1 maxed troop in the other 3 colours if all 5 heroes are to be fully supported by troops, in consideration of circumstances where one colour can’t be used.
Not if you’re scoring damage, (and rethinking my earlier comment). Even a small proportion of contributed damage on a high rating titan could provide a good yield of loot.
And, as you have clearly figured, loot is far from the only reward in this game. 
I was originally aiming for 3x maxed rainbow for both 2* and 3* troops for tourneys and tiered events. 3-2 tends to be my preferred attack team. Maybe in another six years?
It is always good to contribute even if just a little. it could be the straw that broke the titan’s back, meaning defeat instead of escape. I have seen titans in my alliance escape with so little health left …
I am hitting titans and using all my flags 
The loot has been great and we dont let any titan escape except 14☆s