The idea of Doflamingo beating Luffy wasn't possible for a number of reasons, mainly because 1. he was afraid of someone else and 2. because he was the first real enemy after the timeskip. Luffy pulled out a dramatic new power up, but faltered and we were stuck waiting for one big shot while he literally got carried. Good fight but some meh ideas.
Katakuri also never had any right to beat Luffy, he literally wasn't even the boss of the arc.
Kaido on the other hand, the idea of Luffy beating him solo lasted for one whole chapter out of a 50 chapter saga. We still are only like 50/50 on if he'll conclude the fight. You had people on YouTube for months saying the raid itself would actually fail and of everyone Luffy's ever fought, even Krieg who left him to drown and Hody who left him bleeding out among the people who had him poisoned, etc...it was the only fight where Luffy was like "I thought I was a goner."