Usually playing as Byz, I find vassalage to be the absolute BEST way to shield myself from the Western European aggression. By beating both Venice and Hungary into the ground until they accept vassalage and then giving them back some provinces (+ conquering some new provinces for them) sems to work like a charm: I have a bunch of buffer states on my western border, who are very docile and submissive., yet other European powers are reluctant to attack my vassals as well as my empire (not sharing a common land border seems to be a biggie in reducing their aggression against me).
The best part yet is that tribute money is pouring in while I have zero worries about building up or garrisoning the provinces that get sacked and gifted to my vassals.
Nothing makes Byz feel really imperial like a bunch of lackeys and underlings manning my western front.
