For the bike threshold, it’s not really about the resistance. It’s about dialing in the correct cadence (90 rpms) at whatever resistance this requires. That said, I would hope that you have made some improvements! So celebrate them! It wouldn’t surprise me if you said that you didn’t gain any fitness (ie higher LT) due to the volume that you are under and we aren’t really training your higher zones. Since you did, you gained a whole lot of lactate threshold conditioning!
For Ironman training, you can’t afford to have your zone 2 too high. This is a straight line to overtraining. So, yes, I would error on the conservative side. Or I would retest (!!). Remember that this tests have a learning curve just like HR zone training. The better you get at executing the tests, the better you will get at proper race pacing.
Another good discussion David! Are others finding success with HR zone training this season? What is your experience?