Both for me as you cannot really NOT do trad, there are times when it is the only option - as in builders cleans or internal work -
I think it is potentially tougher to come into window cleaning via the WFP route without any trad experience as it is a skill all window cleaners need.
When I used to employ people (in the distant past!) it would take them a good 3 months on average to get the hang of trad window cleaning skills, especially the squeegee, and even when they did manage to clean a window without getting half a dozen scrims (no microfibre cloths back in the day

) soaking wet, they were sooooo slow!
To begin with, on an average semi (say 12 windows) I would get 10 of them done by the time they had finished 2 downstairs windows...and even then I'd have to go back over them picking up their mistakes!!
WFP will certainly become the main method of cleaning windows for standard repeat cleans as time passes.
Ladders may not be illegal as such, but in the event of accidents at height, insurances companies will wriggle out of payouts by quoting health & safety regulations, and lets face it, if an accident DOES happen then it probably is because safe practice HASN'T been followed...

And then the poor window cleaner will be in all sorts of do-do

If it's on a commercial property so will the owner of the company for allowing the work to be carried out off ladders in the first place!....everyone's a loser...except the insurance companies...they LOVE health & safety

You wait, next thing you know someone will take a WFP user to court for a bit of compo because they got splashed with pure water and will claim for chemical burns because they've heard that the process of making pure water turns it into carbonic acid!!!!

Sigh....
Ian