The thing is 160 -> 120 is not underperformance.
Honestly, I think it would be. That would be 1 extra shot versus mediums, and 2 extra shots versus a Panther based only on hitpoints. But given how the Churchill doesn't have very high penetration, that would mean that the average number of shots more needed to kill Axis armor would be even higher.
With the Churchill's poor penetration alone (105 far pen), disregarding accuracy, that would mean
on average:
vs P4 is 1 / (105 / 180 = 0.58) = 1.7 shots extra
vs P4J is 1 / (105 / 234 = 0.45) = 2.2 shots extra
vs Panther is 2 / (105 / 260 = 0.4) = 5 shots extra
With far accuracy at 0.025 (55-60% chance to hit a P4 or Panther) you could probably add another shot to each of those, but I won't include it because it's impossible to calculate the true accuracy with scatter based misses becoming hits.