You're wrong, he's not above YC. Nothing about their battle is top tier. Luffy is not fighting Lucci at the same level he fought Kaido at.
As I've already said, entering G5 doesn't automatically make Luffy's attacks and speed at a top tier level. That explained to us why most of Luffy's G5 attacks weren't causing Kaido any more damage than his G4 attacks. The greatest benefit to G5 is it allow him to handle attacks better and control the battlefield better.
We saw YC clash and even best top tier during Wano.
- Zoro blocked hakai, bested and scarred Kaido.
- Yamato clash evenly with Kaido.
- Marco clashed evenly with Big Mom.
- Big Mom's power couldn't stop Law's awakening power from piercing her body.
Man, stay real. Even base Luffy was able to fight with Hybrid Kaido, even base Luffy partly overwhelmed Kaido. When Kaido started to go seriously all out, only then we saw that Luffy ultimately stands no chance,
until Joy Boy absolutely
played with an all out Kaido. Kaido managed to fight his way back into an equal fight but eventually Gear 5 was just too powerful and destroyed Kaido within
minutes.
There is no way in hell, a non Top Tier character is able to fight and clash with Joy Boy. Its not only about Feats here, in this chapter Lucci was
portrayed so immensely powerful that Luffy
saw the need to use Gear 5 (he never uses more than needed in fights) on Lucci - and we know after Wano that Luffy even without Gear 5 is a
Low Top Tier. Not only that, the reaction from the crowd was another portrayal feat: Jinbei running, Sanji sweating, Vegapunk talking about the absurdness of power Devil Fruit users hold while we see Lucci and Luffy in an equal powerful clash.