He's not talking about the Belgian league though, but about the PL. And the logic stands, if it has been done, it is 'easier' than something that hasn't.
I'd love us to win 4 in a row. And I think it is harder. Obviously either would be great, but for me 4 would be greater.
Say if we weren't to win it, the earliest we'd be in a position to even discuss it again, would be in another 4 years. Having had to win it 3 in a row first. For the CL, that's 2, and having to win it only once. For that alone, it surely is harder.