The switch element in the QCA9531 inside the AR750 is non-blocking, so it’s sufficient and has more than enough bandwidth for all the LAN ports - if needs are simple, it’s more than good enough…

Key thing perhaps on the AR300M as an AP - plug ethernet into the WAN port vs. LAN port, otherwise you might get into a bit of a mess there…

Once set up - configure the AR300M appropriately according to your needs.