Advice on Lucky Bag Summoning

Sabers- no
Archers- you have one of the best ST archers in the game as far as I'm concerned. Euryale np5=Orion np1, Arjuna basically for farming, Tesla is quite good and will get stronger this coming year
Lancers- roll for waifu or husbando If you want to. I want Karna primarily but would be happy with lanctoria or alter. I like enkidu's lore but like you, not a fan of his cards. You don't have any of them or 5 star lancer. Karna and Merlin are a good pair.
Berserkers- you have best. I like vlad and have him max bond. He'll get stronger next year, fantastic with Tamamo and another arts. Not ideal pair with Merlin. Nightingale serves a purpose I suppose.
Casters- they're all great servants to have.
Riders- you don't really need but 3 out of 4 of them are great
Jack/Jeanne- they both do their jobs fantastically, neither pair with Merlin ideally. Jack's c. Stars can mostly be replaced by a fragment or 2 of 2030, a Merlin NP, and some other servant skills.
Tldr; I'd go for lancers as 2 of 3 pair well with Merlin. Even Enkidu has a buster np I think and produces c.stars. You're chances of pulling Karna or any specific 5 star servant (33.33% or 50% for Jack and Jeanne) will never be this good again. although I'd strongly consider casters and hope I pull Gramps lol

You seem to have thought this through fairly well so here's my two cents:

Lancer: Karna, Artoria Lancer, and even Enkidu are usable as you have Merlin. Enkidu is a bit of an oddball but he can still work with the right team.
Rider: The banner I am personally going for. I have no 5* Riders and the Riders here are strong so its a no-brainer. Yes, even Medb. She may be the weakest of the 4, but her 1st skill especially is decent against enemies that like to debuff. Also, no matter which Rider you get, they all benefit equally from Merlin, as they have a QAABB deck with a Buster NP, which means they synergise better with Merlin. This is the main advantage they have over Kintoki Rider with his QQABB deck and Quick NP.
Caster: Can't go wrong here. Having your own Waver or Tamamo means greater flexibility in team-crafting without having to rely on friend support. Sanzang is not as good in comparison but she has her niche in killing assassins.
Assassin/Extra: You have a 50% chance to get an idiot-proof assassin that remains relevant in the future. But you also have a 50% chance to get Jeanne. I don't like stalling teams either and stalling teams are spelt J.E.A.N.N.E. You don't seem to like lolis anyway so this banner doesn't seem right for you.

My opinion: Go for Rider or Caster banners. No matter who you get, it will be a decent choice.

(1) Lancer banner isnt that strong, that is true, Artoria and Enkidu required very good team composition. But the thing is, you already have Merlin so that is fine. Particularly, there is no strong SR lancer except Artoria Alter, but you dont have her.
(2) Rider banner is a gamble. Although 75% chance is quite high, but 25% is saltty enough.
(3) Sanzang is still one best as offensive caster and provide decent team-wide support. Off course, you may consider Cu Alter or other Berserker can provide more decent Buster damage, but Sanzang could be extremly good with Merlin. Other SR Caster wont provide any comparable firepower even Nursery.
(4) I also dont interest in Loli (my MHX bond point is more higher than Jack though they came in the same time), but Jack is extreme good, very versatile in team, and you are quite lacking of Assassin.
Also Jeanne is a symbol as stall team, but it doenst mean stall is her only playstyle.

Overall, it is recommend for you to roll Caster gssr, then roll Grampa. Karna will be in banner next March Iirr. But you still need good Assassin, although Waver/Tamamo are first priority you need.

go for the lancers :either you get karna a great aoe servant or enkidu(belive me he's one of the best last man standing servants i have ever seen:he is really selfsufficient and with a little setup he can be deadly) the lion king isn't that good but she is still an incredible farmer
If you still don't like this banner then go for assasin

Since you have Merlin I'd say go Lancer. Then roll for Gramps . Especially since you're a sensible, anti loli person. Caster is good too, but it didn't sound like you cared as much about getting them. Rider as well, but since you have Kintoki it's not as big of a need (as you pointed out).

What i think you should pull on:
-Lancer: To fill out that hole
-Rider: There are 3 pretty damn good servants (and 1 thot)
-Assassin/Extra: It has Jack and Jeanne
Based on what you said:
-Lancer: I still think you should *consider* this since it seems like this is the biggest gap in power level compared to your other servants.
-Rider: I understand that Medb seems like a pretty big "get away from me" atmosphere, but you have a 75% chance of getting something good (2 being really good)
-Assassin/Extra: This wouldn't be a bad option either, though if you don't like Jack cause she's young, don't pull on this lol (Jeanne can't take you as far as Jack can in this game).

Why I would avoid these banners:
Saber-they're doo doo outside of Altera which you already have
Archer: You have probably the best Archer servant in the game
Caster: you have the best Caster in the game
Berserker: Best berserker in the game...