The factions that really blob with AT mostly is Allies in contrast to Axis in my experiences.
It is usually only in team games that I really ever counter such AT blobs.
Rating from top to bottom, the usage and likelihood of infantry acquiring handheld AT equipment.
Take it from a 4v4 scrub like myself.
Regardless of performance the main offenders for AT inf blobbing are the OST. No idea why but there is a plague of players who spam them.
Doesn't bother me though as I play mostly ussr as allies so they're a simple katyusha barrage to make run back to base or drop if you get a few good wipes in.
With the UKF/USF who lack nondoc rocket arty they can be a greater pain to deal with.
The REAL villain in this situation isn't the blob it's usually the awful pathing of the vehicle trying to escape it/stay out of range.