Exertion is different for everyone and you're obviously comfortable with how certain power levels feel to you. That said, it's quite common for a power meter on the bike and the power reading from a trainer display different output.
There are a number of factors that go into this but in the simplest terms possible, the power reading is likely accurate, within the respective manufacturer’s +/- range, where it’s being measured. Meaning the power level read at a set of pedals will inherently be different from the power level something like a hub, or trainer reads. There is also the +/- difference in range to consider for each individual meter – if they’re each to opposite ends of their tolerance spectrum, that will widen the gap between the readings.
Drivetrain loss/variance is also something to consider, especially when comparing readings to something like a wheel-on trainer like the M2. Power travels through the drivetrain, through the spokes, then the tire, then finally onto the roller on the trainer.
Interference can also contribute - if multiple power meters are in close proximity, there can and will be some competing data that is being transmitted. We recommend pairing the trainer to the Saris Utility app (iOS/Android), performing a calibration, and then an ERG workout with no other power meters nearby or transmitting to verify results. This can be built off of as a baseline.