Are there meta builds that dont require expansions and will get you into WvW groups?
For zergs fights (small or large): I can only think of Elementalist. Although Weaver e-spec is more slippery and dishes out higher damage, core can still be played, and on this class, it seems to be the closest to its actual zerg variant, Weaver, more than a Guardian or a Necro imo. However, not all commanders will accept you in squad during calm times, and even those who accepted you, might favor the ones with meta classes if the squad is almost full. There is no meta for core builds in zerg fights though.
For small groups/solo: You can play almost anything, there actually are core meta builds for small/solo roaming (groups). There are quite viable options as Sw/d thief, d/d elementalist, GS and axe/sh warrior, LB and GS ranger, condi engineer, sc/p and staff mesmer, sc/wh and staff necro and bursty guardian.
So, you'll find viable to meta builds in roaming groups, however, it's unfortunate that there aren't any meta core builds in zergs.
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what auburner said
you can definitely enjoy wvw with core professions.
elementalist is still okay, can pull its weight
mesmer can still support the zerg with veils (invisibility) while focusing on single targets
necro is far from optimal, but still does something
the bigger issue is the gliding and the mount, amiright?
without these two, you will be left behind very quickly. you will be missing out some tactics. you will have longer ways to run and when oyu eventually catch up with your friends, the fight might be over already.
solo roaming is different imo - a couple of professions are able to disengage and engage quickly enough-ish.
I would say core warrior, guard, engi, and ele are your best bets. here are some example builds (sigils chosen are for the best survivability).
guard burn - definitely let ppl know you are playing burn guard and that you only have 1 source of reliable stability.
this website has many meta builds. remember that you can change things up a bit, but not too much. before you start changing things too drastically, its good to know what role you expect to fill and if this role and build will support your team as much as possible.
If you are vocal in comms, let ppl know who you are and what you're running, you're a lot less likely to be kicked or assigned to the pug party.
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I think the bigger issue is not having mounts. Ele and guard can still do fine in large groups, but if you're not fighting around objectives that are close to your waypoint you'll not have a great time running back to commander on those 2.
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You can use core guardian and provide support during zerg fights.
Nothing of what's been mentioned will make you "get into WvW groups" if we are talking about the average primetime zerg. Its more likely to get you kicked.
But other than that, pretty much anything work in smaller random squads.
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