what are u talking about ? flare mines are super efficient, they easily wipe green for 60 muni
That's why i almost never saw how pro-players used this "OP" ability. Maximum 1-2 flare mine in the whole game (4 cons+ 2 engeeners and 2 flare mine in the whole game - very popular ability). Regular mine much better. I think you saw how in 1vs1 champ 1 tm-35 killed 4 wounded pgrens with srecks and CPrice lost the game. Engeeners have flare mine, more than enough.
I told it some time ago - flare mines is heritage of old, cold times, when blizzard mechanic was default. It gave to SU good vision when blizzard started and darkness came. But now it's just "never used" by regular players ability, like medkits for grens.