Are Alakazam and Gengar still useless?

Yes ,they are useless.

Alakazam currently has the highest DPS moveset in the game. It's very time-efficient at taking down gyms if you're good at dodging.

I wouldn't say they are useless but they more useful for prestiging rather than attacking. It's always nice to have at least 1 of each with the best moveset. If you don't have enough attackers, you can power up 1 but not both. I prefer attacking a gym with a variety of mons rather than an army of 6 vapes/dragonites/exeggs.

You are useful for preserving your spot at the gyms since their high CP after the update.

(In the following context, by "Gengar" I mean Shadow Claw/Sludge Bomb Gengar; by "Alakazam" I mean Psycho Cut/Psychic Alakazam)
Gengar is still not useful, but Alakazam is one of the best attackers now in the game.
In most scenarios, there will always be a better choice than Gengar for attacking, in terms of both DPS and total damage output.
On the other hand, until now no other Pokemon can take down Poison types and Fighting types faster than Alakazam, even Dragonite. In some cases, Alakazam takes down Snorlax even faster than Dragonite.

Both are terrible at defending gyms. There's only one purpose of putting them into gyms: showing off.

So you should be happy to have a generic killer in your team.

Alakzam is not only useful, but is one of the best attackers in the game. Gengar less so.

I have a psycho cut - shadow ball alaka with 2400cp+ I use only pcut because need to dodge all the time. Still usefull with only psycho cut?

I was skeptical too about Alakazam, but after getting a psycho cut psychic one and using him I have to say, if you can dodge well he is a really fantastic attacker.