This is pure whataboutism, but to call Starmer - a rabid member of Labour Friends of Israel who has parachuted an Israel lobbyist into a safe seat, and who plans to staff his new government with pro-Israeli stooges - "tepidly pro-Israel" is beyond disingenuous.
I'd ask you to consider that the situations in Syria and Ukraine are not nearly as straightforward as the US would have us believe; indeed, the US and Israel are, as usual, the main instigators.
Regardless, Corbyn hasn't "crossed any lines" - he certainly hasn't publicly stated that it's OK to cut a civilian population's water supply as collective punishment, for example. Corbyn takes a more considered, nuanced, sensible view on world politics, which unfortunately doesn't play well with our right-wing press's simplistic "good guy, bad guy" gov-sponsored narrative. This is why Corbyn was smeared - he stands up for what's right, even if it means going against the US and Israel.