Reason to max SC Gengar?

The most prominent defenders resist this moveset heavily. That said, this is one of the highest neutral dps sets and makes a good counter to psychic types, though they can be dealt with without ghosts. Gengar was really a fad for Alakazam solos and a glass cannon for Mewtwo with Psycho Cut. No way of determining what moves a raid boss may have anymore, Alakazam is no longer in rotation. Not much reason for investing further atm

I use my 82% Gengar all the time. I used him on Tuesday for Mewtwo and I used him this morning to solo Starmie. Not a bad investment.

Admittedly his uses are pretty niche, but good lord is it a monster when it gets used. I have a 12/15/12 SC Gengar at level 35 that I use against FB Mewtwo and other Gengar raids. I haven't had a chance to but I'd love to get a shot at using him against an Alakazam raid. If you're good at dodging charge moves it's an absolute beast. Who knows what raid bosses the future will hold but if they have a ghost weakness and a moveset that Gengar resists I'd heavily consider its use there.

There's no reason to max out a Gengar right now.

That being said, I'm clutching a pair of decent SC Gengar (78% and 87%) that I've got up to Level 35 and hoarding Gastly candies to max these two out eventually. I'm holding out hope that they'll become useful outside of Mewtwo with Focus Blast EX Raids and occasional other Psychic-based Raid Bosses. (I actually used them a couple of times in Latios/Latias raids when we had huge groups and it was a double-dragon moveset. Yeah, they fainted fast, but I got 2-3 SB's off with each, which was nice.)

Gets you way ahead of others during an EX-Raid. In a way, you're competing with others for premier balls during EX-Raids and Psychic-type Tier 5s but that's only for the competitive players.

I use my (lvl 40) H/SB 91% (15/13/13) ALL the time as an opener in Psychic raids. In fact, according to Calcy, it has my highest DPS against almost every target, including Kyogre. It's squishy as can be, so I only use it as the first (sometimes second) slot. I can only imagine having SC...

Maxed two 14a/4/15 and 14a/10/12. I get a lot of Mewtwo invites and now I do those with 3 (or 4) in a private group. Tuesday with 40, 34, 34, 30 against C/SHB won with 119 sec left

80K dust I would say go for it.