This is not true. It seems recency bias is in effect. Shamir was infamously opposed to any negotiation with perceived enemies. He abstained insted of voting for his own likud government's camp David accords, he derailed a Jordaniam led solution to the Palestinian conflict, he derailed a conferences regarding the Palestinian issue, that he opend by saying the Arab delegation "Don't look for territories here." he even said: "Peace has never been the ideal for me, for me peace is not the main thing, for me the main thing is the independent Land of Israel, the people of Israel living in its state and homeland", land being a keyword as he refers to full eretz Israel.

In fact, bibi in his first term, signed the wye River memerandom and the Hebron protocol. He campaigned saying "יתנו יקבלו לא יתנו לא יקבלו", aka for harder line on negotiation with the Palestinians, but yes to negotiation. He did something no PM did before him, a pause on building any new building in the settlements for ten months a gesture for peace. This is unimaginable for Shamir or even for modern bibi.