You can move them sideways to make a wider 'ole y'know. Woodworkers on the Continent have used slot mortisers for a very long time - as have furniture makers/manufacturers here.
Maybe so, but if you ever go out on site being able to pick up several of those "daft" boxes clipped together in one hand while you take your hand tool tote in the other is a major plus, But you do have to buy into the "system" to benefit from it. Fortunately a few manufacturers other than Festool have, e.g. Hikoki, Metabo, Mafell, Lamello, Makita, Deros, etc, etc. It isn't all bad
I wouldn't agree that it's a one trick pony - it solves a lot of problems for a lot of people at a lower cost than a mortiser and a tenoner. I'm the first to admit that it isn't for everyone, though