Hello!
I'm on the newer end of the spectrum, so if this has been reported already please let me know --- but I've been wondering for awhile why my full Primal () Synergy teams don't seem to do so well in Arena and I think I just figured out why with this last game, the final Primal synergy does not seem to be activating properly in combat. It actually dosen't apply any poison at all if you have a full Primal team set up.
This report is specifically for a full Primal team with 5 total Primal () Synergy, and not the lower 3 synergy version - I will have to test if that one activates properly the next time I get a chance to see in Arena, but I'm pretty sure it isn't acting properly either because even enemy teams with Primal synergy did not apply the poison to my team like it should. I will post an update about my 3primal test when I do it!
Anywho, details about what I found below!
Preview of my team's synergies and build for proof I should have the full build:
Examples of first-turn combat that should have the 5-turn poison pre-applied, but enemies do not (any poison displaying is from auto attacks that started up before I could take the screenshot):

Because of the inherit debuff of basically not having these synergy bonuses my team was losing to enemy teams with much less synergies (2-3 synergies could easily defeat me as compared to my really awesome looking 7 synergy symbols) in their teams.