The case for Gasol being cooked:
-He'll be 36 in January
-He was unplayable on defense against Boston's pick and roll
-He shot 42.7% from the field in the regular season
The case against:
-He's still good from 3 and a good playmaker, certainly better than Howard.
-He was injured last year
-As noted, he's barely had a break in two years (although given the nature of this offseason, he may not be rested now, either)
I think people are also forgetting just how effective Howard was as a backup. It's understandable given his clownish nature and that he last made the all star team 7 years ago, but in 19 mpg he averaged 7.5 points, 7.3 rebounds and 1.1 blocks on a ridiculous 72.9% shooting from the field. Gasol gives them things that Howard cannot, but the reverse is also true. Howard is also about a year younger. It's far from a given that Gasol is an improvement overall, even if it barely matters in the playoffs when neither guy is playing at the end of games.
Schroder is 100% an improvement over Rondo in the regular season, but playoff Rondo is a real thing - can Schroder provide the same support in the later rounds? I don't think it's clear.
Maybe Harrell's performance in the bubble was an aberration, but given that he's an energy guy, it wouldn't be a surprise if he is more effective in the regular season than in the playoffs, when the competition is fiercer and everyone's effort level goes up.