There is two other questions to be asked:
Is the way MVP does overmold enough to make a difference? Cross sections showing how much core mold is in the rim makes me believe there's oppritunity for them to improve. Fission is a good move in that direction and possibly is closer to showing some practical differences. (Same weight, as similar as possible PLH/dome discs seem to fly differently, yet grip/human error are still factors)
If there are tangible benefits to increased gyroscopic effects, are those effects a positive for all desired flights? Do discs with less "gyro" change directions easier making some shot shapes easier?
So, I think the gyro effect, when compared to non-overmold discs is fairly negligible outside of Fission, but I do think Fission has a bit more of an effect. I try to be as scientific when I compare things as I can. So I am always comparing the PLH of my new discs when I buy them to the same mold when I have them before I ever throw them. I like to compare them both right side up and upside down to see dome, PLH, and all the things. So when I compared my 164g Fission Crave to my 160g Neutron Crave, and they were nearly identical, I expected them to fly pretty similarly. The Neutron flies very true to numbers, with -1 turn and about 1 fade. The Fission just goes straight, very little turn, very little fade. And I've noticed it really tends to lock onto whatever line I put it on better than anything else I have. If I throw it on anny, unless I give it a bunch of height, it just holds it to the ground. If I throw it on hyzer, it doesn't hyzerflip, it just rides it to the ground.
My Fission Envies also seem to get just a little more distance and still hold their line longer in general than my other Envies. They don't really fly differently than other Envies though otherwise. But Envies are by and large pretty HSS.
I think the problem is, Fission plastic is probably the least consistent plastic MVP makes. Whatever happens to it when it cools, probably something to do with the microbubbles, probably causes it to tend towards understability, because more often than not, Fission discs come out with a bit more dome and lower PLH and can get pretty flippy. But that's the difference in wing shape, and not in gyro effect causing it. So the data isn't really consistent enough for us to know for sure, but, tldr, minimizing as many variables as possible, I think the gyro effect of Fission is a real thing.
As to your second point, yeah, I do think that might be a bad thing sometimes if it's not what you want. I prefer my Neutron Crave over my Fission one for my turnover lines because it will pan out easier and not turn into a roller while still holding a negative bend a long way. But, for shots where you just want a long straight tunnel shot, you could do worse than a Fission Crave, that's for sure. Even if the current blend of Fission is slicker and stiffer than I like.