No, disabling the SSIDs (even all of them) does not actually shut down the radios. You can also disable the hidden meshing SSID as mentioned earlier, but there too it will not shut down the radios. Note that on the Radio Settings page, you can turn off the 2.4GHz radio completely. But the 5GHz radio minimum is 1dBm. So if 5GHz, sounds like you would need to shut down every-other AP by disabling PoE on the respective switch ports, would probably be easiest & fastest.
However, if you're finding that there's way too much overlap and the APs are all tuning themselves down to only 2dB, and you have a high density deployment, sounds like 500+ devices in the same room, then the best way to deal with that is directionality. That is, in a HD deployment the primary design priority is spectrum re-use, and the best way to achieve that is with directional antennas. Pretty standard for auditorium and lecture hall or exhibit floor type of deployments.
If that's not an option and you'll have to use the APs you have on hand, then you'll need to keep fine tuning to find the sweet spot. Be sure to try using 20MHz channels on 5GHz, go with 12 or 18Mbps minimum bit rates, and only after you've done all the standard fine tuning, you can then also play with RX-SOP, but only do that like 1 or 2dB at time, then re-test. Leave time between each tweak, and run Update Auto Channels, and give that time to run. There are built-in delays by design to prevent an unnecessary ripple effect of channel/power changes across the network, so run it overnight for example.
Also, if you're not using meshing, then disable it. If that option is not visible on the Network Wide > General page, call Support ans ask them to enable that option in your Dashboard.
I'll assume you opened a Meraki support ticket earlier, and they did a scrub of your current config with the model of AP and the firmware it's running, just to rule out any known issues? You might also try toggling the Client Balancing setting on/off, and possibly band steering on/off which has on occasion caused some strange disconnect issues, but there too, it's a function of AP model/chipset, firmware version, and client device make/model/drivers. Will take a bit of trial and error to really narrow that down, but Support can assist.