Half wifi speed via EX3700 than direct wifi

That's expected. here's the reason why.

Extenders have to recieve a signal and then retransmit it. And it has to do it with the same chip in standard extender mode. This means the bandwidth gets cut in half and the latency is higher than a direct connection.

this can be mitigated somewhat with using fastlane on the dual band extenders or going with a triband extender. Fastlane and tribands reserve a radio just for router---extender communication. 

Again, in standard mode, that's how extenders work. They're great for extending distance but they do so at a speed/latency penalty.