SB is better in the meta. Celebi, mew, mewtwo, even outperforming psychic vs ho-oh.
Damage without SE:
200-3,2s CD = 200-(74(C) or 53(PC) = 125 or 147 (+SB being more flexible)
100+20stab= 120 damage + Around 30 (C)to 40 (PC) energy
So raid wise and in a neutral gym fight without SE, SB outperforms P.
Actually, there's no relevant mons in the metagame weak to psychic, in the main series psychic type is a bad offensive type, it only has two type advantages (Fighting and Poison) and none of them have a very strong representative Pokemon (Till 5th gen) the only good mon of either of the two types is Machamp, so you only want psychic attacking mons against him
And my guess is that the two ratings were done by two different people with different opinions, preferences, and/or methods of evaluation. There are many inconsistencies in Gamepress's moveset evaluations.
Also the moveset rankings for a mon are supposed to be independent of what other mons can do; they are meant to be an internal comparison of the mon's movesets relative to each other without regard to movesets of other Pokemnn.
On a similar way, would you think C/SB is better or PC/SB? I kind of like fast quick moves and I wonder if there is a big performance difference between both of them. Not talking only about dps of the fast move, but a combination of both fast+charge, which one is better overall C/SB or PC/SB?
Depends on what you're fighting. If you're using Mewtwo as a psychic counter, PC is better as you'll get to SB faster. If you're using him as a generalist, C is better as it provides higher cycle DPS.
Also take into consideration what feels better for you. The difference isn't that significant between the 2, so if you find you hate how slow C is, use PC; if you like slow, hard-hitting quick moves, use C.