Servants Worth Leveling

Generally, no. Herc trumps all.(at least the servants u listed)

All servants are worth leveling, even if they may be low tier because you'll never know when you'll need specific servants from a certain class in various events/challenges.

Nursery Rhyme is a good offensive Caster that works well on Arts and Quick teams and can pair up well with a Jack, which both will be able to dish out crits all day. Plus she also has good survivability to boot, a good boon against Assassin nodes.

Marie Antoinette is a good support tank, and can help keep your Herc alive especially if you equip her with a taunting CE. And when everyone else is down, Marie can help you out on the last stretch of a battle due to her staying ability outlasting any remaining enemies/bosses.

Beowulf has a really strong Buster NP, which also generates a good amount of stars allowing a combination of NP and Buster crit attacks, especially handy when he's on the back line, and can work well with Herc as cleanup crew (or if you want either Beowulf or Herc to be on the frontline while the other Berserker is your backup damage dealer/clean up).

If you have maxed Herc, the only zerc you will ever need is Raikou and Cu Alter (and I guess Kiyo, as she is cheap and a good farming machine, as well). I think you can burn Beo.

Marie is a Rider AOE, she is the Cu of the Riders, with Invincibility instead of Evade, also constant self-healing. Maybe, test her a little.

Nursery is AOE Caster, like Nito; but without instant NP bar full skill (just +40% NP on lv 10 with Meanwhile) and no Instant Death powers; yet her Self Modification A paired with a passive star generator (Innocent Monster/2030/MLB Hot Spring Under the Mom/Anniversary Heroines/etc) can make her deal some quality crit dmg (who help to fill her bar quite easily), while having Morph A+, who makes her more durable+a 1K to 2K heal skill (the other effect on Meanwhile). And her overcharge NP effect is 20% Def Down for 3 turns+decent chances of removing 1 dot of enemies gauge, which is very nice on a AOE NP.

She's for farming, you can pair her with Nito, or if you think she's good enough for farm all alone, you can burn her.

Nr is good, but difficult to use fully. Marie is good with a 2030 or similar. No need to use beowulf.

Some event in the future will have them as event bonus servants and you'll wish you had them. :)