My Mavics use Ocusync, not WiFi.All DJI drones (and most others) use WI-FI to connect the remore to the drone. The Spark also uses it to connect the remote to your tablet / phone *unless you are using the OTG cable thing.. You really need to check all your WI--FI settings no matter what drone you're flying to get the best signal.
Different communication systems, provide different range, latency, video characteristics, and multi-connection capabilities.
WiFi settings of Spark, provide a manual channel selection, to eliminate interference, but in populated areas it's difficult to find a free channel.