Overall, I prefer the 1400 to the 1010 as a more versatile router. But if all you are doing is jig work and dadoes the difference doesn't matter much.
For jig work, you want a light router with a low center of gravity to avoid tipping the router. The 1010 is better on these two scores.
Unfortunately, most jigs are not designed for dust control. I have tried using the 1010 on a porter cable jig and find that jig knobs and such interfere with the dust control accessories on the router. Don't know if this is the case with your Leigh.
A possible deal breaker is that the 1010 will not accept 1/2 inch bits, but I presume you can use 1/4 or 8mm bits with your Leigh (but be sure before you buy a 1010).
The two should do equally well on the dadoes.
To tell the truth, neither of these uses need a plunge router. If dust control isn't huge for you, consider a PC690 - perfect for jig work and will save some coin.