On the XL: the 0.6mm makes sense with the build volume, to significantly improve print times, but seems to really not work well with the 5 toolhead models, and introduces massive amounts of zits, stringing, cross-contamination, etc.
On the Mk4: at the price point, it’s maybe missing a few features to really hold up against the X1C, maybe even the X1E. Spaghetti detection (camera support), klipper, real input shaping, etc.
On input shaping: Prusa bet on the wrong horse with input shaping. Adding a <2g sensor to the toolhead was the right solution, and generating default input shaping profiles based on models in the factory was not. Most Prusa customers would’ve been happy to add the part themselves. Now they’ve sunk so much development and money into this, they refuse to accept it was the wrong approach and switch gears.
Klipper: Marlin is old. Sure, it’s amazing what Prusa is able to squeeze out of it, but at some point, the tech debt is just going to hold you back too much to be competitive. That happened around mid 2022 for Prusa, and yet Prusa decided to push 3 new printers on the same ancient firmware.