I hear this a lot. Or that Leopard or Snow Leopard was peak Mac. That part of the debate doesn't interest me.
What does interest me is that pre-Lion software is well understood. The behaviors and expectations and commands are re-implementable. Isn't it time someone just made SwiftUI-Tiger or somesuch?
Heck yeah, I love using my 10.4.11 Macs. 10.6.8 as well, of course. To me those two were real high points in the life of OS X, thus far. The computers themselves were still super cool and had a lot of character, too -- another thing that has gradually faded over time, IMO.
10.4 Tiger
They started to ruin the iCal user interface in 10.5 Leopard.
In general, 2006 was peak Mac. When it was Apple main product, before iPhone.