I agree, i got a new ac86u few days ago, was using ac68u before that, i had more free memory on my rt-ac68u than this newer rt-ac86u. I have on average 72mb of free ram and this has double the ram compared to my ac68u. Currently ac87u reports used ram: 440MB, free ram: 72MB Total: 512MB. Before installing merlin firmware it was approx half of the ram free. Although i am not criticising merlins hard work or anything incase someone suggests it.
But you seem to have much more free memory than i do, yeah i run ab-solution, dnscrypt, skynet, 1 vpn client, want to run another vpn client and a vpn server but will have to see how my memory manages it all.