Leman man, i'm not suggesting anything! This post is to explain why it's slow. Give an answer to the question only.
The problem is how you arrive at your evidence. Don't forget that the sources you take compare desktop RAM with different performance characteristics. I think that we should be very careful in extrapolating from there. For instance, here are some other results:
https://browser.primatelabs.com/v4/cpu/1077988
https://browser.primatelabs.com/v4/cpu/794505
One is the 2016 MBP (16Gb LPDDR3 2133), the other one is Dell XPS 15 (16GB DDR3 2133), using the same CPU. I am using Geekbench (even though I am very sceptical about it), as we don't have anything else to compare. I also picked two results from the top of the respective list (basically top results for each laptop/OS). Note that the MBP scores much better in RAM bandwidth. So what is the truth here? Is LPDDR3 faster after all? I honestly don't know. To find it out one needs to take a MBP and a comparable DDR4 laptop (e.g. the XPS 15), sit down, and do some careful memory testing. Everything else is just idle speculation.