Make sure the TP link is accessing the external antenna. ( I dont know if the spark have firmware limitations ) I dont know if 5G uses MIMO like 4G but @coffeebaron should be able to help on that one.

The TP-Link X50 5G is a neat alternative to using fixed line broadband in ... 4G and 3G cellular data at theoretical speeds of up ... a 2.5Gbps WAN port and two external antenna connectors. TP-Link.

As a wireless router, this is an AC1200 specification dual-band service, and the mobile comms are 4G+ LTE-Advanced, with a theoretical throughput of 600mbps down and 50mbps up.