Now we are going of topic (again 
)
A jumper will (perhaps) compromise the signal integrity of the signal path which is crucial in the high frequency range.
Here is some first hand information
In my experience the range of the ESP12F module (on the wemos board) is better than the external antenna i used together with an ESP07 (with correct jumper setting). The pcb antennas on some TTGO boards (not using the ESP12) was good but not as good as the ESP12 module.
Reading the document the problem seams is not the size in general it may be more the design and the placement. I place the antenna on the far corner of my designs outside the mother board pcb and avoid cables all over the place. The pcb antenna might be good but if you place shielding all around and ontop of a pcb with ground planes and what not no wonder that you don't get the possible performance. An external antenna help here. Comparing the two zigbee coordinators (one bare pcb and the zigbee 3.0 plus) I have the same results.
Perhaps I got totally wrong tuned antennas which could happen (mentioned in some sources) and no way to measure the tuning.
But with my decent APs all wifi problems are gone (forever). So I don't have to spend any affords here.
