Yes you are right, HR cannot change the resistance of your trainer, only power target can.
I would suggest you use a power plan, or find a way to get power (with speed cadence sensor and a trainer curve) for more reliable workouts.
TrainerSpeed is the speed your trainer is sending to the software (raw speed from the trainer)
Trainer speed does not give you much information and is used to calculate the power if you are using a power curve.
MaximumTrainer speed, or calculated speed, is a speed calculated with the power output you are generating.
It can look like outdoor speed and is an estimation of that based on generic outdoor variables.
For now the software only support ANT+ sensors, many sensor offer both bluethooth and ANT+ support.
Sorry if that does not answer your question, there is no plan to support bluethooth in the near feature.
Yep, that's what I thought and expected but both of my straps behave the same. I could do with another head unit to test with but I sold my old Garmin Edge.
Quick free ride below shows the output from Maximum Trainer. HR strap only connected to laptop (MT) for the first 2min and then also connected to Garmin 735XT from 2min onward which had no problems with the HR reading. Definitely an odd one.
Did it several times, no error anything. It looks fine and here the ping on my phone the link to strava is up and ready and nothing ever shows up at Peaks. I re-installed twice no change. I get the account linked confirmation.