Superbazooka
Occasional Visitor
..Yeah that's the big problem with 2.4 wifi. The slowest client on the network will drag everything down to its level speed-wise whether it can communicate faster or not. That's why 5 is better if you have a choice.
In your router admin page, network map, View List - You can see all the clients and their connected speeds. I would bet your really SLOW 2.4 clients in the list are the newly added light switches
That last test i did I had 7 things connected but out of the 7 only 1 was on the 2.4g network...the laptop i used to test it. I switched to my phone and connected to the 2.4g network and tested it just now and got 27.9 down and 13.7 down. and had my laptop wifi off.
I just now added 6 items to the 2.4ghz network and retested and im getting 42.7 down and 17.4 up. This is weird.
And under the wireless clients, it is jumping from 8 total connected to 2 to 4 to 7 back to 8 clients and just keeps jumping around . I managed to get a pic of it though.