First of all: Which protocol is the most accurate today or in other words which Powermeter unit is the most hightech? Cyclus2 or SRM i guess is still the line … and even here … I saw powermeters which show approx. 30 W lower over time because their strain gauge were less accurate (especially the case when heat or cold is involved - temperature drops/ups).
Pedals are different to crank spider measuring units. I’m pretty sure many Smarttrainers don’t show exact values by different temperature and higher wattage to each other. The point is: if you want it even more serious too much effort is involved to stabilize reliability.
Still the question of all question to this case is: Which is the most accurate powermeter?