Its normal..
2 batteries and a buck driver is the good high output solution.
In single cell (or parallel setup), cells with low voltage sag is the best option if you are seeking max output, but you get lower capacity and runtime..
The largest difference between XM-L to XM-l2 I have seen was 3,5 to 2,2A. In that case, I switched back to the XM-L since I did not care for efficiency in that light. Your result is quite typical.
I shared some various results in the L4 mod thread about the issue I had with Vf on different XM-L2s. Either way, XM-L2s in general need a bit higher Vf...