Saying Joker is just a clown is like saying Batman is just a dude playing dress up in a bat costume.
A great villain doesn’t necessarily mean “Oh, he’s just as strong as the hero”, it’s someone who can attack the hero where their weakest and most vulnerable.
Batman believes life is sacred and is fueled by the powerlessness he felt watching his parents die as a child. Joker is the perfect villain because he tests Batman’s willpower and conviction, not because he can punch hard.
This is a great villain.
Perhaps I can see where the issue is now.
So... to me Batman is the guy that fought with Lady Shiva, fought Superman and Darkseid, knows over 120 fighting styles, had the guts to go into darkseid's planet while no having powers, has perfected both his mental and physical shape and is the world's greatest detective. He is great and even powerful in that manner.
But.... when he fights the joker he is vulnerable in those stories.
It's like when he fights the joker it's a different batman, not the same as I described above.
So he's maybe his match when he's that batman.
I dunno, maybe thats it