BKool software just isn't up to scratch.
I had a similar experience - 2 people (one of which was me) produced the same average watts per kg for the session and he finished in just over half the time I did.
I asked Bkool about this and their response was 'There is more to it than just Watts'... !!... perhaps so, but to produce this much discrepancy?
There certainly is more to it than just watts, as discussed many times on the monster thread.
You mentioned average watts per kg for a session, which would only be a sensible measure if the session was one continuous steep gradient, with no near flats or downhills. On the flat, watts per kg mean next to nothing, just pure watts is what counts!
Drafting means fewer watts are needed for the same speed, so if two riders sat at the same speed the second rider, in the draft, would need many fewer watts to achieve the same speed/time.
If you push hard at high speed, your watts are used to overcome exponentially increasing drag, so gain less and less time. If you push hard at low speed, such as on a steep gradient, then drag is much lower and you will gain more speed. If you pedal hard on a steep downhill you are mostly wasting watts, for perhaps very little gain. Fair enough if you have power to spare, but then comparing watts or watts/kg is far from the full picture.
So it is as much about clever use of power, knowing when to push hard and when to rest, than outright power or power/weight.
Having said all that, some results seem too far out to be sensible, and are just as likely to be down to differences in the simulation for the two riders as any power differences or strategic use of that power. For example, the latest bkool firmware changes have made the simulation very different, and in many respects much harder, but not everyone has or can apply the latest firmware. Some bkool trainers are stuck on very old firmware which gives great advantages to those riders.
You are not always playing on a level playing field!
Indeed, it is difficult to see how a truly level playing field could be produced in a simulation using such a range of uncalibrated hardware.
Since there are so many differences, and it is easy, for example, to lie about your weight, you can only really take it as a bit of fun, a way to make otherwise tedious training time much more interesting.
If you want real competition, I'm afraid you have to enter real races in real life!
Cheers,
Geoff