Did a quick search in this forum for “Rumble issues” and came up with 1600 results. I know it’s not an accurate accounting of Fender’s QC record, but it’s far more than just a blanket statement that you feel Fender’s QC is better than Ampeg’s.
Own few rumble combo from 1st gen to 3rd gen, never meet single issue. Try BA 150 and 210 v2 at GC, both have loud cooling fans and the BA 150 driver start distort/fart at 3 o'clock volume. My rumble 200/150 still sound strong and solid even 4 o'clock volume.