The reason I ask is that Lanza is quite possibly the hardest IM bike course there is and it looks like conditions were a bit harder this year than the previous year. Looking at some of the splits from athletes who rode this year and last, even at the front of the AG fields they are often 10-15 minutes slower and the longer you are riding the more disproportionally you are affected. I try to keep an eye on my AG results and one guy who rode a 5hr bike split in Kona (in a normal weather year, not last year when times were stupidly quick all round!) rode just under 6hrs in Lanza. Obviously I’ve no idea whether he had other bike issues like you did but there are other riders whose times are significantly slower than I would expect.
A 5% difference in conditions for a 4hr rider can mean a 12m slower ride which translates as a 24m difference for a 8hr ride and that doesn’t take into account the fact that winds generally tend to increase as the day progresses which again will disproportionally affect those who are on the course for longer.
One other thing to keep in mind is that the PD curve and IF calculations are time based rather than distance based. If you look at the often quoted chart for expected TSS and IF for Ironman splits and translate that ‘good’ range for tops out at around 66/67% for a 6:30 ride. If you continue that charts progression to the 8 hour or so mark then and IF for a ride of that duration isn’t hugely unreasonable.
There may well be other factors at play as you have suggested but I’m trying to look at some of the other context around the day and what may or may not have contributed to a ‘disastrous’ ride! Power is great, as is other data and the predictions it can make but it’s you that needs to push the pedals around… sometimes life gives you lemons and it’s uphill and into the wind!