Difficult to say in general. What GL-inet network mode is used?
Look (again) via Luci to the packet flow.
LAN ethernet ports are connected via the switch and are in the same VLAN? So flow is only ethernet-switch-ethernet, and is supposed to be at wire speed. If the switch is cut-through capable and enabled, there is even no store&forward delay for the packet.
For wifi and for home/guest networks the packet must also pass the CPU chip. Software there can be "bridge" for devices in the same subnet, or can be "router" for different subnets. As @Tomkatt mentioned, then also firewall and all sorts of NAT/mangle/masquerade and filters and limits may apply.
In my setup above LAN1 and LAN2 are both connected to the same VLAN on the same switch, and hopefully transferred IP packets never enter the CPU. A CPU may use/delegate some switch features with "hardware acceleration", but LAN-WAN traffic passes the firewall if those interfaces are part of LAN and WAN zone.
You need a bridge or router to connect over 2 different VLAN ID.
When "Network Mode" is set to "Access Point" , then the Switch remains with VLAN.id 1 and 2, but "LAN ethernet ports" LAN1 and LAN2,(both on switch VLAN.id=1), connected via 'eth0.1', and the WAN interface connected via 'eth0.2' and the home wifi interfaces named 'wlan0' and 'wlan1' are all bridged via bridge 'br-lan' . Guest wifi is not in the list.
bridge interface br-lan:
