I think the problem is more likely to be your metagame, not galaxxus. A mage that tries to protect the sslaks and use only one orb is susceptible to swarms. If you destroy his galaxxus and get out enough creatures to overwhem the enemy who is using galaxxus, you should be fine.
I've read and reread your post a few times, and I can't really get my head around this. The early metagame is mainly shaped by the rules and card pool. Perhaps it might evolve with many plays within the same group, but it will start by perception of card strength and what cards best contribute to your strategy. Assuming [mwcard=MWBG1J05]Galaxxus[/mwcard] is legal, if you want any hope of winning by V'tar (and in multiplayer, you have a much greater chance of winning by V'tar than by eliminating all other mages), then you must run Galaxxus. And if you are first to get Galaxxus in play, your primary strategy is going to be to protect your Galaxxus and/or the orb(s) you control that allowed you to cast Galaxxus. Your back-up plan (e.g. if your opponents make a tremendous effort to take out your Galaxxus) might be to take additional uncontested orbs... but only in extreme cases where your opponents put a considerable amount of resources into taking out your Galaxxus.
The "cause" is the existence of Galaxxus; the metagame is the "effect." It isn't the other way around. We don't use Galaxxus because of the metagame. The metagame exists because Galaxxus exists.
I'm not a Mage Wars playtester so I have no idea if this is true, but I suspect that Galaxxus was originally "Warlord (or War mage) only" - partly because the Warlord is thought to be under-powered in Arena, and partly because it makes sense thematically (the orcs and/or dwarves found a way to replicate the power of the orbs, as per the flavour text). Then the playtesters/designers realized that the Warlord kicked butt at Domination if he was the only mage who could use Galaxxus, and that the Warlord was actually pretty good at Domination even without Galaxxus, so rather than scrap Galaxxus entirely, they opened up Galaxxus to every mage (but kept it War school both for theme and because "hey, it's got to belong to some school so might as well be War and benefit the Warlord slightly more than other mages"). But it's so overpowered and, after a few matches, everybody discovers that it's absolutely crucial to a successful V'tar strategy (seriously, try winning without Galaxxus against somebody that has Galaxxus and let me know how that goes for you), and it will shape the meta all on its own. Even a Druid will gladly pay triple for Galaxxus, partly because she is among the best at protecting it.
Net result: Either (1) get used to the fact that everybody has a Galaxxus in their book and the first person to play theirs will generally win (unless s/he gets killed), making outcomes of matches predictable beyond round 3, or (2) ban Galaxxus and make your multiplayer Domination matches more unpredictable and fun for all players. If your experience is different, then I congratulate you... but I don't see how this could possibly be limited to - or due to - our local meta. It's pretty much ingrained in the Galaxxus card text and rules of Domination.
One thing you can do is nullify the sslaks that your buddy build opponent wants to protect. also, warlord can use harsforge monolith to great effect. turn to stone has upkeep +4. That's really expensive to maintain. If you put enough pressure on them and force them to use their mana in other ways, the turn to stone will come off and you can have an easier time attacking the ssllaks. Deathlock will counter all bull endurances on sslaks simultaneously because it's life gain is not innate. You could also use rusts on the sslaks, or acid balls. or just dispel the turn to stones. or you can curse the sslaks and use DOT to kill them. it's not that difficult to destroy galaxxus, and it, unlike the wizard tower, is actually costed right.
Although I haven't played domination much lately, so I haven't tried all these things myself.
I've considered Turn to Stone and other "protect Sslaks that enemies attack" types of strategies and they're very hard to pull off since they take so many resources that could otherwise be spent trying to secure your own orbs. It falls into one of two categories: either (1) player(s) C (and D) benefits when player A spends resources preventing player B from acquiring an orb, or (2) it's a "win more" situation where you're so far ahead already that you can afford to waste resources stopping your opponent while also acquiring orbs on demand.
I'm not sure what you mean about [mwcard=MWSTX2FFJ01]Harshforge Monolith[/mwcard] being something worth playing in Domination. In my experience, Enchantments don't see nearly as much play in multiplayer Domination as in Arena, so either I'm missing something or you meant another card.