Ok, it is not a true "single lens" but there is a good chance that you do not loose 50 % of the initial
All the macro lenses you just listed do not use internal focusing, so your point is moot. I did not argue against macro lenses in general, only against macro lenses with internal focusing.
Modern lenses bend the light by crazy ways so there is a chance that you simulate lens positions to get
1:1 without loosing any focal length. Think about EF-S10-22 at 10mm which leaves 35mm space between back lens and image plane!
These lenses do all kinds of crazy stuff, but when it comes to focusing they are still as they always were: internally focusing lenses which forfeit focal length at MFD for elegance, and lenses that maintain their focal length but become longer as you focus closely.
I own the 60mm and the 100 mm USM Macro-both do NOT extend and use (including the 180mm Macro) after Canon's USA home page a
"Focus Adjustment: Inner focusing system with USM"
- so I do not understand your arguments - or is there a difference between "inner focusing system" and "internal focusing"?