He refused to lift the cap on child tax benefit that the Tories set to 2 children only.
He made the
pensioners' winter fuel allowance means-tested - only available to those on benefits for the very poorest.
Both of these have been hugely unpopular in the party - the latter so much that he succumbed to pressure and gave the allowance back, for the coming year, to more people.
No, Corbyn is not "into the politics of grievance on the left as much as Farage is on the right". That kind of both-sides-ism, when one was the former leader of your party, is nasty triangulation. Your own sentence says this - "no one whines and complains like Trump and his (blessedly few) imitators". Farage is a Trump imitator; Corbyn is not.
Starmer has declared Palestine Action, a group that trespasses and vandalises property that is used to build arms for the Israeli military, but doe not target people, a terrorist group, despite the lack of terror (in the targets of Palestine Action, that is - plenty of terror in the targets of the IDF). This means that saying "I support Palestine Action" is a crime. He has had over a thousand people arrested for doing that.
The problem with "pragmatic thinking" is that it often ends up being "do what the opposition would, to 'claim the centre ground'".

To be only +13 among your own party's voters is not good.
Among all adults, his polling is now 72% "doing badly", 18% "doing well". Among Labour 2024 voters, only 44% say the country is going in the right direction:
https://archive.ph/xSqDS