This list kind of terrifies me.

https://geordanr.github.io/xwing/?f=Rebel Alliance&d=v4!s!41:27,-1,110,-1,-1:-1:-1:;254:27,120,126,243,-1,237,-1:53:25:U.239,u.-1;275:170,166,-1:-1:-1:U.-1&sn=Unnamed Squadron&obs=

It's got Fenn Rau doing Fenn Rau things. The Nym harpoon, Ten triggering the harpoon condition immediately, plus the Sabine and bombs mechanic going on. All at PS10. Why is this not a thing?

Initial engagement I don't see it erasing something off the board that first turn. Unblockable crit from a single action b-wing is just a single crit. Single harpoon at PS10. Fenn's 2 dice. Its not like the double PS11 imperial Alpha with twin Harpoons and a 3rd shot at PS10 or OL. Or Nymranda with two harpoons and a bomb off Trajectory Simulator. I'm far more scared of those. I'd be more worried playing as this list that Fenn dies first, followed by Ten a turn or two later. Or Ten the first turn from 2 harpoons and something else. I could be very, very wrong since I've not played against the list though.

Nym just gets blown off the table on the initial joust or the turn after it. You need something like Miranda to double alpha with or something to take the heat off Nym. Nym has terrible defenses for the current meta and once he is off the table, Ten is just a B-Wing and Fenn is just a support piece.

You’ll nuke something if you can get the harpoon off with Fenn at Range one, but then he’s at risk if splash damage. I’ve seen people do similar though, and it’s nice to see people trying to fit B-wings into lists.

I think this list is "not a thing" because it was built to put meta-gimmicks into a squadron list without actually building a meta list. Nym is likely dead in the opening joust, Ten Numb soon to follow. There are just too many Harpoon Missile builds to keep Nym alive and too many TLT builds to keep Ten Numb alive (and a few lists that do both ).

As @Estarriol said, it is nice to see a B-Wing in a squadron list.