Exactly.Also remember opportunity costs. Ie. you lose "physical bulk" with assault vest since , unlike leftovers, assault vest does absolutely nothing when facing physical attacks.
Offensive assault vest goodra also "loses" the extra offensive power it would have gotten had it run something like lifeorb.
Just something to considder.
252 SpA Rotom-W Hydro Pump vs. 252 HP / 0+ SpD AV Goodra: 37 - 43 (9.7 - 11.4%)
Given that Leftovers heals 6.25% per turn, AV only gives more bulk on turns where it takes a special attack doing at least 12.5%. When taking physical attacks, resisted/weak special attacks, or no direct attacks at all, Leftovers comes out ahead in bulk.
Personally, I tried AV Goodra initially, then decided to briefly try ChestoRest instead. Even without ever using Rest, I barely noticed a difference in Goodra's survivability against attacks I was actually letting it take, aside from Ice Beams from Greninja. With neither item mattering much, why not use Leftovers?