First
Thank you for the math
Second
Glad you kept that purple troop.
As Rook has said many times, keep all your high rarity heroes and troops, the Devs are always tweaking under and over used heroes and troops.
In this case the new reflect blue event hero changed the game, and reflect red and reflect green still haven’t come out yet
MY PERSONAL OPINION
In general, a 3* lvl 3 troop is better than a maxed 2* lvl 15 troop and a 4* lvl 1 troops is better than a 3* lvl 9 troop, so I keep three of every 3* and 4* troop for use with my 3 color teams since you don’t even have to level a 3* or 4* troop to have them become immediately useful, see above, but if you don’t have them, you can spend hundreds of summons trying to get them back, this is a lesson I learned with my duplicate Banes.
It will become a lot easier when next non-bug update rolls out ( Devs have promised the ability to favorite troops ).