No other right-click ability has a cooldown, and putting a gun mode on shift/E is weird. It doesn't fit the design philosophy.
Just remove the instant reload on roll and up the reload time a smidge. The double FTH is what deletes tanks. You'll still crush squishies as intended, just no more overpowered E, RMB, Shift, RMB.
Lucio's right click has a cooldown instead of his shift.
Also, fan already has a longer reload time than his normal reload doesnt it? Not really a cooldown in the strictest sense, but still.