You are right, the visitable interface and the sealed class are comparable. Good point!

Why be a big fan of something so restricting?
Haha, that’s like asking why use a strongly typed language and not Javascript. Or move to C or assembler, no restrictions at all. ;)

In the end it’s about choosing the right tool for your job and then stick to it without taking shortcuts. For me OO produces great software if used correctly. For others it’s functional programming or a mix of both. Discussing against a preference, hat’s a war going on for decades that can’t be solved :D