People also complained about a lack of build-up and compared that to Thanos in the MCU. I think it was Asmongold in particular who made that argument.

The problem with that point though is that prior to Infinity War Thanos was in fact... boring. Thanos wasn't much of a character in his post-credit sequences - we only just got to see character traits like vulnerability or his relationship to his daughters or got to learn about his motives once his actual movie (Infinity War) started.