You have a solid point, but I am a plan believer. I really just want to do the prescribed workouts.
I should do this though or manually drop my FTP. I’ve been scrolling back through my old training recently to see if I can understand my shortcomings. My biggest weakness may be plan adherence on the weekend. A close second that I can see now because of the recent changes is the pauses I was taking during threshold workouts. I always knew they were hard on me, but I thought I was still completing them “successfully”.
The Half Iron and all triathlon plans are a bit different to the cycling plans - you don’t get AI recommended volumes or structure, but you do get AI workouts.
So - as AI is setting your workouts based on power and not FTP there is no ‘growing into’ a new FTP, it would recommend the same workouts although the workout duration may change. Consequently I would not change the zones based on feelings.
However, you aren’t getting that assessment of how much bike you need to improve. As a triathlete myself I’ve compared Tri plans to bike plans, and I found that I can get the same or better FTP gains on lower volumes than most or the Tri plans. I’m only doing Olympic distance and we’re different athletes so it won’t translate directly for you, but it’s worth playing with.
That should give you a better sense of how long your hard sessions should be. I suspect it will be shorter, 1hr mid week.
To find out, just start a new custom plan at the end of your existing plan, and play with the settings.