No. if you are a skilled 125 rider up against a 250 rider of less skill than yes, you can beat them.
the 125 gives up about 3 foot pounds of torque, and a couple of horse power.
the 125 has its ups and its downs in comparison. Way lighter, alot more fun! better handling..... it doesnt throw the power to the ground as well as a 4-stroke.
if you are riding sand i'd suggest the 125. jumps up on top of the sand better and doesnt nose dive down under engine braking.
better re-sale value, easier to work on, cheaper to repair......
125 2 strokes suck for trail kinda. If you can ride a 2 smoker through the tight bush you will be 10 times faster on a 250f. I had a 125 2 stroke but now im ripping it up on a 250 thumper. I think 250f's are better for jumping. youve got that bottom end for coming out of the corners, and there easyer to controll. it personal prefrance realy.