Yes, Uzzah sinned seriously, yet ultimately, it was David’s failure to maintain proper respect for God’s Law that brought about that tragic outcome.
وَلكِنْ رَغْمَ أَنَّ عُزَّةَ ٱرْتَكَبَ خَطَأً خَطِيرًا ،‏ فَإِنَّ عَدَمَ إِظْهَارِ دَاوُدَ ٱلِٱحْتِرَامَ ٱلْوَاجِبَ لِشَرِيعَةِ ٱللهِ هُوَ مَا أَدَّى إِلَى هذِهِ ٱلنَّتِيجَةِ ٱلْمَأْسَاوِيَّةِ .‏