R6220 set in "Access Point Mode", slower download speeds ?

> Because then I have a Wi-Fi hotspot in my room, [...]

   Ok.  I know nothing, but my first hypothesis (guess) is that the
(non-deluxe) R6220 is too slow if you use its WAN/Internet port for the
connection to the main router.  If that is the problem, then I see two
possibilities:

   1. Use a gigabit/s-capable network switch for the speed-critical
wired devices, and connect the R6220-as-WAP to that switch for your
(less speed-critical) wireless needs.

   2. Try using a different WAP configuration scheme for the R6220,
which does not use its WAN/Internet port.  See, for example:

      https://community.netgear.com/t5/x/x/m-p/1463500

   That's written for a Netgear C6300-as-WAP, but the steps are about the
same for any other router (any make/model) which lacks a one-step WAP
option.  If the router which you're reconfiguring has a WAN/Internet
Ethernet port (unlike a Cxxxx), then leave it unconnected.

   You might see some odd (but minor?) problems that way, like, say, the
Internet LED might not look right, or the R6220 can't find a time
server, so its date+time might be wrong.  I'd run the experiment, and
see if the wired speed improves, and then see if there are any
significant problems.  It should be educational, at least.