Defending against two GCs on first node wave of your entire team is formed right and you picked the more defendable node is not too hard. No battle highs or LBs yet, so it's usually a stale mate at worst. The hard part is the transition into the next wave of nodes - turtle strat for one wave may win you the battle but cost you the war. Especially if both sides keep you locked into a corner while they hold all nodes and are picking off stragglers.
For the past two months on primal, Maelstrom is the dominant GC. A bunch of good PVPers moved to Mael from Flames and when they play its no contest. They are organized, have sound strats, and do not tunnel vision - rather they're looking steps ahead at all times.
Flames when Clean Up Crew is at full force are comparable, they have better combat ability but tend to not be as sound in their strategy. They've lost some close matches due to focusing on the kill rather than best course of action.
While some of the best individual PVP players are on Adders, they can't compensate for idiotic decision making and actions of the majority of the team. Adders either lose in spectacular fashion, the competent groups don't get their act together until it's too late to recover, and the 8 wins I've seen in 3 days of aggressive PVPing were a fluke (Mael/Flames get into vendetta mode and ignore nodes and Adders) or the stars aligned to have a majority of good and competent players actually in a match together.
In Mael, it was common to win a majority of the time, and usually if not we got 2nd. 3rd rarely happened. Flames would win more consistently when it was CuC time, but overall wins came slightly slower than when in Mael. Also more 3rd place finishes.
In Adders so far, if it wasn't for my rage quits this week, 3rd place would be double the amount of 2nd place finishes. 2nd is the next most common. Wins are at...maybe a 20% rate at the moment. It's taken me around 40 Adders matches to get 8 wins.
Now, each GC has its ups and downs (Flames sucked the first two days I was in them, so could be another similar thing happening here). But word of mouth and talking to people with dialogue to the larger primal PVP community with the best players has given a lot of anecdotal evidence that Primal Adders are just bad in Seize. Different story in Slaughter and Secure, apparently, but nobody plays those modes anymore.