Sanity Check on my Unreliable WiFi: Do I Need More Access Points?

[big_spaceship]

TLDR: ZD1200 with 9 r710 APs covering 21K sq ft macOS-dominant biz, constant connection issues. Would more access points actually fix the problem?

Long form: I took over an existing enterprise network, consisting of an Untangle, 1Gb switches of various makes and models, and Ruckus for the wireless. The Ruckus consists of a ZoneDirector 1200 and 9 r710 Access Points, on a dedicated switch connect to the Untangle by 1Gb ethernet. The office is a rectangular 21,000 square foot space in a dense mixed-use urban area, with over 100 different wifi networks in range (I'm counting 2.4ghz and 5ghz separately here). We are a macOS-only shop with an average 100-150 devices on our primary wifi, and the same on our siloed guest wifi (total wireless device count rarely tops 300 devices). 

I get daily complaints about wireless not working. The most common issues are failing to connect after waking a laptop from sleep, AirPlay not working, and wifi appearing as connected but not transferring data. None of these are reliably fixed by toggling the antenna or restarting devices. 

Here are some of the more significant changes I've made in an attempt to reduce connection issues:

• Reduced channelization from 80MHz to 40MHz
• Reduced channelization from 40MHz to 20MHz
• Capped the maximum devices on any AP to 50
• Physically moved a couple of the APs to improve coverage
• Disabled the 2.4GHz spectrum on all APs except one for specific devices (did it by disabling WLAN service on the 802.11b/g/n radio)
• Modified every Mac's default connection preference to be the AP with the strongest signal, not the last AP accessed (which is the default)
• I added a script to the most afflicted computers, which keeps the antenna turned off for 5 seconds after waking from sleep
• Note: TX Power is configured to Auto, but all radios always run at Full power anyway

There are some other specific tweaks done for increasing compatibility with Apple products, but I've been working on this for over a year and I can't recall every detail. And as it's been over a year, the boss had demanded a permanent fix regardless of cost. That opens up my options in terms of adding access points or even switching to a different vendor. 

BUT: I have enough hardware on paper to completely control my airspace, and I don't think more access points will "solve" anything. If I succeed in fixing my network just by overpowering my neighbors, they'll be forced to do the same. I do not want a wifi arms race. 

Any suggestions?

[big_spaceship]

The best solution I've found to improve roaming on Macs is pushing this shell command to them:

/System/Library/PrivateFrameworks/Apple80211.framework/Versions/A/Resources/airport prefs joinMode=Strongest

More info on the options available here:
https://apple.stackexchange.com/questions/66919/how-to-enable-faster-wifi-roaming-with-mac-os-x-airp...