they were all perceived as the anti-establishment option.
Not sure about this. Johnson may have folded some Farage into his campaign, but they were still the party that's been in power for a decade.
Starmer's reluctance to criticise the government
He's definitely been critical at times, I think he's trying the tactic of 'dont interrupt your enemy when they are making a mistake'.
Starmer could be steering toward a 'sensible' centre ground that Blair occupied for a while to win back some conservative votes. It will upset some on the left and I'm not sure he has the charisma to pull it off even though he's technically skilled. Also Johnson is best at turning things into a pantomime, where he's happiest. Perhaps Starmer is the 'safe pair of hands' before a new leader comes in? The same way the Tories washed around before Cameron/Osborne. Things can change pretty quick.