Just a few thoughts
1) I agree that 5 GHz is becoming very widespread
2) However, 2.4 still needs to be treated appropriately
- Number of client drivers still do not behave well with band steering and do not necessarily select 5 GHz
- 2.4 should be deployed with the power set 5- 8 dB less than 5 GHz radio in the same chassis
- the extra chains make the link more robust due to diversity benefits
- If you get a DFS event the 2.4 needs to be properly tuned to preseve your customer experience.
- 2.4 should generally be left on to ensure anyone connected to 2.4 is on the nearest AP and getting a decent user experience
- Turn off your b rates and even a couple of the low gn rates. This reduces the beacon time consumption and improves 2.4 performance.
So even if the 2.4 band performance is less than 5 GHz it is still 60 MHz of spectrum that you have access to and, deployed properly, adds value to your end customers.
If PoE is a constraint, then as someone mentioned AP-215 is a great option outside of higher density areas.