This was my recommendation but, again, I wouldn't do it inbound. Especially no taxi from BTS for b50.
I'd not actually timed it and yes, sometimes taxis will get choked up in Lak Si, but I think taxi for me faster.
Departing, I just walked directly north and out then a nice walk to the Pink Line.
I think the shuttle TO BTS is out the east door and the wait like 20 minutes.
An absolute godsend if you get stuck out there late.