Originally Posted by
rubiksoval
We know because we have actual power meters.
Yes, many times.
Can also get an idea from comparing group rides from similar riders with and without power meters, or even comparing strava segments.
Suffice to say, it isn't an argument. Estimated power is absolutely nothing to pay attention, to. Anyone claiming it's "not that bad" simply doesn't understand what affects power, and why even small deviations can impact training and performance if power is being used for that.
It's a matter of perspective and expectations, I think.
You're right that it doesn't have any value when it comes to actively training. But when it comes to tracking progress of someone new or newly-invested in cycling? I think that the window of error is too wide to put any stock in "analysis" of shorter efforts or even single rides, but, in aggregate and paired with RPE, it may be all that they want or need - some kind of affirmation that they're trending in the right direction.
Should someone strut around at the café stop because Strava estimated that their last ride averaged ### watts? God, no. Would I recommend a power meter to anyone more with than idle curiosity and the means to scrape together a few hundred bucks? Yeah, for sure.