the whole count your reward expieriment-part is unneccessary. Straight to the topic:
Rewards for Recruit and Vet Battles are fine. Only Legendary could use adjustment to the credit multiplier ( T5 modules cost more Credits then XP so that would be fair i think).
I see the issue in the combination of long queue times and short battles, 1 hour of ingame time takes 1 and a half to 2 hours in real time because you spent a lot of time idle at the hangar in a queue. Even more punishing is the battle bonus cooldown, which actually keeps you from playing taking into consideration that you don't get your free BBs as soon as you start buying battle bonus.
My suggestion to shorten the idle times in the hangar would be to just remove the battle bonus cooldown at all [just to clarify i mean the battle bonus multipliers basically count every battle], whoever thought of cooldowns between matches : it is a terrible idea .
If on top of that the credit reward for legendary gets increased that might be a motivation for more players to queue for legendary resulting in shorter queue times.
At the end its all down to the devs and their economical plans, but i'd rather have players who enjoy the game and thats why they buy stuff than players who buy stuff to be able to enjoy the game.