How is it more annoying? It's the same thing. Pull the cable, fish a new one. Or if a housing is needed, pull the old housing an fish a new one. It's no different than other internal routing systems. I have it on my 2023 Scott and I ran a dropper post housing/cable without disassembly of the headset. Same as internal routing through the frame. What are people talking about??
How many people here are simply regurgitating what the read on the internet vs actually working with one of these systems first-hand?
One of the most legitimate complaints I've heard is that having the opening on top of the upper bearing may lead to more dirt/water intrusion into the upper bearing. I'll buy into that.
The vb-099 I have is headset routed with internal handlebar/stem routing. Looks cool, no cables hanging out anywhere on the front end. Huge pain to work on using a full mechanical groupset, but at least there's no cables.
Headset routing on a mtb still has cables in front. The cables just go into the headset a few inches up instead of into the frame. Which makes maintenance more annoying. You can't replace your headset bearing without also buying a new olive for your rear brake. Plus disconnecting everything else. Really not that common of a service, but it's still more work for marginal to no gains. Things break on mountain bikes fairly frequently and personally I'd rather not have to deal with more annoying things when fixing stuff. Headset routing for mtbs just doesn't have any positives imo.
That said it'll still probably become more popular like internally routed cables simply because it's cheaper for manufactures.
Guerilla gravity and Deviate have cool solutions for cable routing that make life easier.