LTE is already pretty darn fast, so losing a little performance isn't going to make that big of a deal. It's not as if you can torrent to your hearts content without killing your cell phone bill.
The issue isn't just speed. It's also range.
At any given speed, the Qualcom can support it at substantially lower signal levels. 6ish dB in a lot of cases, a bit less in some, enormously more in others.
Look at the graphs in TFA. In addition to some specific pathologies that penalize the Intel chip farther, the bulk of the graph has the drop off looking similar but with the Qualcom shfited 5 or 6 dB to the right. (Those squares are 5 dB wide.)
6 dB is four times the effective signal strength, which corresponds to twice the range. That maps into four times the area served at that speed from a single cell tower (important in sparsely-served areas), deeper penetration into buildings and the like (in more heavily-covered areas). It can also map into more data pushed before a given area and channel allocation's bandwidth is saturated. 3 dB corresponds to twice the effective signal strength, 1.4ish times the radius, twice the area served.
If the modems were equivalent and the problem just the layout of the board and antenna, you'd expect the two curves to be the same shape but just offset. The shape is substantially different, so (board issues or not) something else is going on.