Katakuri's personal view on the matter are just that, HIS opinions. Luffy had no problems in getting help from others in most of his post TS fights so does that mean him defeating Doffy "doesnt count"? And yes the fight would go down differently if Flampe didnt interfere, but that doesnt mean that it would end in Luffy's favor since until this moment he was getting no consistent hits on Katakuri, it was only after Kata dropped his spear and injuried himself that the fight began to be more equal so as far as we know Luffy would be more likely to lose if Flampe didnt interfere
Luffy wasn't trying to grow to overcome Doflamingo and lots of that battle was riddled with PIS to keep the drama up/ show off G4's weakness when KKG would have oneshot him.
If you are making a hypothetical "who is stronger" matchup then of course the fight scenario should be taken into account.
Luffy was learning FS at that very moment, the turning point happened in 891 and in 892 Katakuri began to acknowledge there was a chance just as he was getting drugged...
Basing Luffy's performance on before the turning points of these two chapters, in which Katakuri himself began to acknowledge the growing threat is being unfair to Luffy.