I’ve absolutely no idea if I get more power when using oval rings as I’ve no power meters on any of my mountain bikes. However if I get better traction (as in less spin-outs) then I’m assuming that I’m wasting less power than with a round chainring.
Taking times off Strava is fraught with difficulties especially off-road as there’s so many other variables that unless one time is significantly faster, say 10% quicker, then as far as I’m concerned, it’s just a time that might be quicker but it might be slower.