Put the original points mag back on to prove a point just incase you're chasing the wrong end of the stick.
I think you could move the timing around a bit from 2.9 & it would still rev regardless. The factory setting of 2.9 isn't an exact setting as in how high it revs--within reason,--but if you went back to 2mm it might sound like its struggling to rev out as its getting a bit retarded--a bit like me lol--& now i've forgotten the rest of the story!!.
Ok looking back you have a 250 so 3.2 btdc is factory, but if Rex's say 2.9 they must have variations built into the electronics for when it running. Be interesting to strobe to a mark with a felt pen & see if it moves to advance more or retards at revs--or whatever!!.

I was happy with the 6v points system until the stator coil open circuited. The cheapest option to fix it worked out be the Rex's speedshop 12v conversion
system, RMK-6. I have had nothing but problems with trying to get the DT running right since.

DASHA, would be good to link a video to youtube if pos.
Be good to hear what its doing--or not doing as the case 'is'.
I'm still stuck with points.
But come to think i have one motor somewhere, a bit of an experimental motor long story.
Bought a DT360A cdi mag with flywheel for $20 where something had gone through.
Think by memory the lighting coil screws fell out with corresponding damage. But the cdi source coil was in with a chance.
Pulser coil was wiped off too. But i had a Plug coil off a Suzy RG50 which is coil & cdi combined combined.
I wired the source direct to the plug coil cdi as only one wire in & it ran perfect for the mess of a motor it was.
I didn't have to time it. Flywheel straight onto the crank key & away we went.
That's on an early RT2 based motor. So funny what works at times. Feel free to fall over laughing at the bike. Cheers.
ps i strobed it kicking to see if it was close then running & was in the ball park for timing.
I actually did exactly the same on a DT125L about 25 years earlier when i bought the bike with screws fallen out of the lighting coil & ran perfect for the kids around the paddock. Any small suzuki runs the same set up cdi & plug coil combines. Is that what's called solid state? i don't know.