This deck would not pass inspection in our area. Was the deck permitted? For one, the band only appears to be a single joist, followed by a composite material on the outside (no visible fasteners). Second, the posts should have cross beams (double 2x12 girder) with the joists supported on these girders (rather than by the band).
Refer to the earlier picture in this thread. This deck has the cross beam (girder is the best description) PLUS additional 45 degree supports for each post. Much stronger! The girders provide a LOT of side support for each post, plus distributes the vertical load across multiple posts, particularly if the girder is cut into the posts ("let in"). For this reason, I always use 6x6 support posts, as letting in weakens each post slightly. "Letting in" ensures the loads are supported by wood, not your fasteners...fasteners hold up the girders, not your deck.
Last, since your deck boards are on 45 degree angle, you cannot use standard (5/4) deck boards with 16" joist spacing, but are restricted to 2x6 deck boards (if PT). I would have built it with joists 12" in center, even with 2x10 joists. I can't tell what you have; composite materials are even weaker that PT.
It's done now, so question is what to do...I'd refer to load tables, pull a permit if required, and add adequate posts and cross beams...you can do this without rebuilding the entire deck. If you don't know how to read load tables, get someone who can (you can still do the manual work, but make sure it is designed and engineered well...do it right!).
Visualize what us happening without girders...a post is only supporting the vertical load of ONE joist, plus whatever load is transferred back to it at the end through the band boards at the end. Currently, your middle support posts are essentially only supporting ONE joist! Add girders across each set of posts...all vertical loads are shared across multiple posts, plus much more lateral support (no sway) for the posts. Girders also make it MUCH easier to build the deck, as you just lay and space the joists on the girder(s) as you build it!
Good luck with it...I've seen much worse in terms of underconstructed decks. On my previous new home, the builders deck wouldn't pass code...but the inspectors apparently focus on other issues when inspecting new homes.
Hope this is helpful.