As Rich points out in the "Info" section, r.e the Diamond Tail:

"This shape moves the release point forward, essentially shortening the outline and rail rocker. ...your 9-0 diamond has only 8-10 of rail line. An even tighter radius turn is the result, but with a little less drive than the squash or square"
This explains why the DT surfs even more like a short board than some other 2+1 high performance LB designs and certainly more so than a single fin (at least in my experience).

"Also, I would really appreciate some more feedback on the single fin vs 2+1 subject"

I agree that single fins will give you more drive and longer, more drawn-out turns. Personally, I'm willing to give up a little drive in each turn for ease of making a series of smaller, tighter turns to "pump" for speed or to make subtle, pocket adjustments. I also do not like how single fins come off the top. Sure, the DT might fall behind at a place like Maalea, but how often do most of us encounter a freight train like that?

I'm too old to compete for waves on a short board any more, so my 9'0" DT is the next best thing. It may not catch waves like a San-O, but it sure out-paddles the 7'4", short board thruster I used to use in larger surf.

The DT is loose w/o being squirrelly in big surf and with a 7" cutaway fin and side-bites, I've never spun mine out while pushing turns.
In addition, the DT bottom rocker is such that I've made steep, late take-offs that would have pitch-poled a lot of other longboards.

All depends on how you want to surf. The DT is a "climb and drop" or "rail to rail/off the tail", as opposed to a "trim and glide" design.