@Yahyoh Unfortunately, thats exactly what it is in access point mode. A not so smart access point.
In a home environment any kind of meaningful traffic control is normally performed by a router. If you have disabled the routing mode this will have an impact on any kind of traffic shaping, parental controls etc.
This is the same with all of the mesh systems I have come across to date as well as modem routers running in bridge mode - they all lose most of the features.
QOS mainly controls traffic on the wan port (internet). If the Deco in AP mode it is no longer controling / routing the traffic and hands the job over to the main router on your network which is connected to the WAN and therefore best placed to perform the QOS.