In this era of frigg flanks and finley wings, is it worth it to ascend JF for this purpose?
Is he a very effective counter to those 2 heroes?
Issue with JF is the offensive part of his skill does not synergise with other reds, and often would outright overwrite other burn DOTs
Depends on how many rings you have, your other reds and your current maxed reds.
Overall I’d say Jean is worth maxing but depends where u you want to use him. For raid attacks he sounds efficient.
I hv 6 rings
Maxed grazul BK c.marj and kong.
Jf QOH and anzogh at 3/70
Not sure which to ascend.
But i see alot of frigg / finley which often wipes my team
You already have BK. That would have a bad synergy with the Queen. Go JF
Also, that team you have will fit him as Marjana-c doesn’t give fire dot
He will definitely do good against Frigg. Not as much as Finley as his bonuses will cause damage all the team. But still, it’ll be reduced as he adds defense against blue so it might not end up that bad at the end🤨
Finley has an effective counter, Mitsuko. As Finley is usually left wing, late charging, I never worry about him. Mits is 95% of the times active when he fires and… fireworks suicide 
Unfortunately, there’s no counter for Frigg… the last part of my wories about her is her defense down… when she fires, there’s usually noone left to have a defense down problem… I would have liked a costume for a blue to reflect green, Mitsuko style… that would have been a counter for Frigg, not as effective as Mits / Fin though, as Frigg is flank, not wing… of course, formations changed this a bit.
You already have cMarj, she makes even a Finley+20 with lv 30 troop hit like a 10 year old. And her fast speed means 85% of the time you can beat Finley to the punch. So in that sense JF is slightly redundant.
That being said, out of the three you listed JF probably has the most utility. QoH is really a poor man’s BK, and since you already have the real BK she can sit at 3/70 for a while. Anzogh is… I dunno, neither here nor there. Attack is a bit too low for an effective AoE, and because of the low attack the healing also sucks, so yeah probably can wait at 3/70 as well.
Finley can bypass Mitsuko’s reflect with his pierce talent now. Granted it’s only 25% chance but still not the 100% proof counter she used to be.
Frigg counter… Garnet maybe? If you’re not worried about the defense down but more the AoE damage, then Garnet’s overheal is just what you’re looking for. Plus she gives ailment protection like Grazul so the defense down gets neutralized as well. Of the overhealers in the game, she’s the only one at charge speed, so she can almost always charge before Frigg barring a really bad board.
Garnet is listed as ultra rare. In gatcha terms - SSR. Not too many in the game has her. 
Agree qoh is poor man’s BK
Anzogh is also like a poor man’s kong in terms of damage
I dont hv garnet, she would be similar to grazul but better because of overheal.
I should probably try my 3/70 jf against frigg defenses before deciding