Bro if anything, hu gong was always more silly???? Like, the whole point is that he was a silly old man but in reality he was actually super cool and strong. I think it’s because there was more fighting and seriousness in the more recent arc that you may have forgotten. Also, now that he got his swords back and is back in the murim alliance, he might be acting more like himself, rather than the young master of the heavenly archive.
I actually think it's improved. I'm not sure if you're an artist but the anatomy improved if anything. The face anatomy was alien looking before lol, but I don't know how far you mean when you say old art style. For me at least, I think he's more "hu gong" and than the young master now. If you reread the flashbacks the current him matches more

I feel like the artist has changed? The artstyle is slightly worse than before, the anatomy and poses... It doesn't feel like the artist is cutting corners, it feels like a different artist trying to adhere to the old art style.
Also the MC's personality in the manhwa as well. A few chapters back the MC was aura farming with calm and cool, now he's more silly, like he gets stumped by his team's and everyone's reactions far more. It feels like a different interpretation of the MC compared to before... idk man am I the only one???