TSR's certainly aren't necessary. Playing games on a computer isn't necessary. Those TSRs are, however, convenient, and, the vast majority of current games don't have problems with TSRs.
Regardless, I went through and closed everything down, and sure enough the flicker disappeared.
If I take the trouble to figure out which program is conflicting, is there a snowball's chance you or someone else at Paradox will go and attempt a fix?
In the name of accuracy, games tell you to turn off all applications during installation - in fact every piece of software I own does that. However, none of them are so bold as to recommend complete shutdown of every other application during normal use.