Since I like a lot of the suggestions, I null voted because I would have chosen more than 1 and none of them would be higher in preference.
Here is a slight take on the "Prof Gain".
#1: Keep maximum to 10 per wave
#2: Make it so you gain +1 Prof point per "successful hit check" to maximum of 10 per wave 100% of the time
#3: Keep in accordance to #1 & #2 even if your character level is below your Rank Level.
#4: To stop abuse, keep with the same rules with healing prof gain... You have to complete and kill a wave before gaining more Points even if you remake game and spawn a new wave etc. Thanks to Bigheaded for identifying this with heal prof gain.
Quite honestly if you think about it, it won't make much of a difference... you only gain max 10 per wave yet most of the higher ranked players need to get like 22,000 prof points or more to get ahead.
01000 / 10 = 100 waves
02000 / 10 = 200 waves
03000 / 10 = 300 waves
04000 / 10 = 400 waves
05000 / 10 = 500 waves
06000 / 10 = 600 waves
etc... BUT, if you are killing off monster waves in 1-6 attacks, then you are only going to get 1-6 prof point gain per wave and NOT the max 10.
Remember, just a thought, and if you think about Rank 15+ ... that is like 16,000 prof points = 1600 waves if not more... each action with normal weapon is 1s, now add up the time you spend or spent if this was suggested.