What Mfr and model and circa is the prior router?
What circa is the Fire TV stick?
What model is the Android devices and circa?
Heres my testing:
IP Address Mode Rate Signal(%)
192.168.0.107 802.11n 135M 80% Iphone 6P 2014 iOS 8.4 supports 867Mb on AC I think. N I presume should be 450Mb or at least 300Mb.
192.168.0.104 802.11n 270M 98% Mac Book Pro 2007 OSX 10.10.5 supports only 270Mb on 5Ghz.
192.168.0.103 802.11n 450M 100% Mac Mini 2012 I think, OSX 10.10.5. Supports 450Mb on 5Ghz.
192.168.0.101 802.11n 450M 100% DIR-865L 2012/3 1st gen AC router in wireless bridge mode.
192.168.0.105 802.11n 450M 100% DIR-865L 2012/3 1st gen AC router in wireless bridge mode.
192.168.0.106 802.11n 450M 100% DIR-865L 2012/3 1st gen AC router in wireless bridge mode.
Test using default factory settings for wireless. Just change the SSID name and set a PW.
Set Single mode N, WPA2 and AES only have the same results as listed above.
I have a feeling that older generation wireless drivers vs new generation wireless driver seen on newer generation devices maybe the issue here.