One thing is struggling against a strong enemy
Another thing is trying your best to beat said enemy, and still lose.
Then proceed to fight and beat much stronger opponents without looking like you're struggling just as much.
At that point, nobody could say how strong Kid was. Luffy had fought and beat Doflamingo (with help, but he did overwhelmed anything Doflamingo tried to do at some point), then fighting Cracker (with help, but that is post Doflamingo Luffy, and he still struggled and had a lil bit of help), then he fights Katakuri, gets a Haki bloom, manages to fight Katakuri in equal terms and (supposedly) wins the fight. That is way ahead of how strong Oda made Law look like.
Since you're a Sanji fan (
), imagine Sanji having the opportunity to fight Doflamingo multiple times, learning all his moves and abilities (actually Law already knew that previously), but he still gets beaten everytime and loses a leg. Then a few arcs later, without doing anything worthy strengthwise, he is on the rooftop fighting two Younkous without much problems, despite struggling, then helping to beat one of them in a 2vs1.
It simply doesn't fit. Oda should've gave Law a Commander level opponent to make us feel like he has the potential.
I could even bring up Zoro, who is a Supernova, he didn't beat anyone worthy of praise like a Commander level character up until Wano, but he got a power up supposed to boost his AP and train his Armament Haki, and went to the rooftop, gave the best he could post-timeskip using Enma and showed Conqueror's Haki, then he fought King, he struggled, got better control of Enma and then got CoC coating, and then beat King in a 1vs1 who has a bounty considerably above 1 Bi. This is an example of an actual strength progression.
What did Law got? Blud simply got much stronger due to getting beaten multiple times in the worst ways possible?