Similar timing? The 251 takes (40+20+30-20=) 70 fuel to get while the Luchs takes (15+45+60-10=) 110 fuel. That's a whole 2-3 minutes later in the average 1v1 match with 15-25fu/m with the occasional cut-off.
The Luchs definitely does not need any worse timing than it currently has. It's rarely used anymore and when it got nerfed with a longer build time ~2 years ago it was practically never seen anymore and it had to be re-adjusted.
The timing of the AEC and the Stuart are debatable. I'd definitely agree the AEC comes out a bit too fast or at least that it kills the 223/222 and 251(/17) too fast. Instead of the dull solution of simply pushing its research time, I'd be in favour of changing its damage from 120 to 100 so that it would increase the shots to kill 320hp vehicles while not increasing the shots to kill of 400hp vehicles (with damage going to 160 at vet 3 for better scaling). That way the UKF would get to keep their fast LV deterrent to compensate the lack of mainline infantry snares while giving the Axis lights that suffer the most from it (223/222/251/215-17) a bit more room to escape it.
I think the 251 itself is absolutely fine though. It's strong enough as it is.
This all seems more than reasonable