dobber is a fantasy hockey ranking, so not really pertinent to actual NHL Value. If you asking who has the potential to put up more points - sure it might be Sergachev. Sanheim will likely only get PP2 minutes while Ghost is around, but Sanheim made huge strides defensively in Lehigh this past year, so it was a win. the Flyers are going to have a lot of good defensemen on the blueline, so i think people may be disappointed that none of them are going to put up huge 50+ numbers consistently, as the workload will get split because we should be able to balance it.
Bleacher report is from 2016, and lists Sanheim as needing a year in the minors to round out his game (which he did). The rest is mostly addressed above.
the TSN report has credence, but even then i have to doubt it as it has Phil Myers above Sanheim and Sergachev, and I'm not sure i buy that. It all lists players like Kaprizov and JEE above both of them, so i have to question the rankings a bit.
The original point made was that they are at the very least similar, which i don't think is really deniable at this point. Im sure Montreal fans would take Serg over Sanheim because they followed him and understand him more, just as we have with Sanheim, and would take him over Serg.