Airtime is the real budget in dense Wi-Fi
A stadium or lecture hall isn't slow because each link is slow — it's slow because hundreds of devices serialise behind the overhead of taking turns. This lab takes one fixed workload (a room of phones, sensors and a couple of big streams) and schedules it three ways. Legacy CSMA/CA gives every frame its own turn with fixed overhead and the occasional collision. OFDMA splits the channel into Resource Units so many small frames share one turn. MU-MIMO uses spatial streams to serve several clients at once on the full width.
Toggle between the three and the same blocks reflow while the total-airtime bar collapses — typically a large reduction for the small-frame-heavy traffic that dominates real networks. The lab is honest about the trade-offs: OFDMA wins for many small/latency-sensitive flows, MU-MIMO for a few big downlink-heavy ones, and a single legacy client keeps forcing a full-overhead turn no matter what.