It's pretty clear that the Power Pack continues the PD philosophy of "top 3 guarantee", which exists throughout the single player. Also, and I think this is going somewhat ignored, the "save game" function resets everything. If you use the save game, you aren't leaving people in the dust. You won't make it several laps ahead of 2nd or 3rd place. I do about 1/2 hour chunks and go back to the races when the mood strikes.
If you want to avoid the top 3 guarantee, you have to go to custom races.
You can see it at work if you use the unofficial Sophy supported cars in a one make race.
Use the bypass method here -->
https://www.gtplanet.net/forum/thre...f-incompatible-cars-1-65.431406/post-14485022
They basically fight around YOU. They try to keep pace with the you, so if you are 20th, 19th and 18th will fight harder. As you make your way up the field, the cars that you've passed seem to somewhat give up on the racing, while the challenge from the higher ranked Sophy cars increases. This is, of course, when the weak boost feature is on. Oddly, the unofficial cars seem to work better than the officially supported cars, so there might be some degree of nerfing.
With the Power Pack, it is indeed forced so that you aren't lapping completely by yourself. Instead, you are passing back markers. I wished they would simply allow emergent behaviour to prevail, but I will bet my life that some executive producer has veto'd any possibility of that.