Is Boonshare the best support build for pvp?
It kinda depends how far in support you want to go. The “traditional” boon-share keeps most of the offensive ability of the mesmer but adds boon support. You can also go for a full support + defensive (bunker) which works particularly decently with chronomancer.
Your build seems of the first type. I would just swap your second signet (illusion) for a blink. I am addicted to blink, and especially since you play marauder, a stun break + mobility/escape is very very needed.