I've been using Adobe design products on a daily basis for around 25 years. GIMP is simply not capable of what Photoshop is. Not even close. You cannot accomplish the same thing on it. As of right now, an alternative on Linux doesn't exist. I've certainly tried to find one because it's one of the major things stopping me from permanently switching.

As for the Ableton comment, I've been a user of Ableton Suite for around 15 years. Bitwig is catching up fast (no surprise - it was started by ex-Ableton developers who were frustrated with Ableton's slow progress), but there's a major problem in that most plugins and many audio interfaces are not compatible.