It’s impossible to be consistent with the star system. There’s no absolute scale only what something achieves within what it’s aiming for.
Ebert gave pregnant Arnold Schwarzegger's "Junior" 3.5 stars ("this macho guy melting with feelings of protectiveness and maternal concern") compared to his evaluation of Clint Eastwood's masterpiece "Unforgiven" coming in at 2.5 on the Ebert scale.
He often valued what he perceived as important social messages over artistic merit.