Will a 5 GHz hotspot from my Ethernet-connected laptop reduce gaming ping spikes?

A faster speed test does not necessarily mean lower gaming ping. If your phone went from roughly 50–60 Mbps to 180–200 Mbps through the hotspot, that shows the wireless link improved, but you should test latency and jitter while gaming as well. The original problem could also be internet congestion, bufferbloat, or the router struggling under load rather than just the 2.4 GHz radio.

Set the laptop to stay awake and use a maximum-performance or equivalent power plan while testing. Disable aggressive Wi-Fi power saving if the adapter’s advanced settings provide that option, keep the laptop close to the phone, and make sure the hotspot is actually using 5 GHz. Also try rebooting the modem and router first, since temporary router or connection issues can create spikes on both Ethernet and Wi-Fi.

The improvement may come more from placing the laptop closer to the phone than from 5 GHz itself. 2.4 GHz can still provide reasonable latency, but it is more crowded and has better range, so nearby networks and other devices can cause interference. 5 GHz usually has more available channels and higher throughput, but shorter range and weaker wall penetration.

It’s worth trying because the laptop’s Ethernet connection would bypass the router’s 2.4 GHz radio. The phone would use a separate 5 GHz wireless link to the laptop, which may have less interference, especially if the laptop is nearby. The extra routing hop through Windows should normally add very little latency, though it is not guaranteed to be as reliable as a proper access point.