So I purchased a few LHG XL 52 ac links and I've never used mikrotik 5Ghz devices before. As I look at the default configuration, it appears wan1 & wan2 are in the same bridge. Wouldn't this cause a loop? Are we supposed to configure the bonding? Has anyone used these yet?

Here is the default config.

The device's default config has the WiFi's in station mode... nothing more and nothing else...
All th rest depend on what you want to do...

There are 2 ways to achieve fail-over, Mikrotik has setup the simplest method in their LHGXL52ac factory default configuration, that is then RSTP (STP tab) which is a system that toggles (switches) itself between available interfaces in its bridge. So the RSTP is designed to stop looping, the RSTP intelligence logic has been programmed to stop packets / traffic looping. For status of the actual used port you need to go to the menu Bridge then Tab Ports where you will see column Role, the port line that has the words "root port" next to it is the used port at that moment. The next colum Root Path Cost shows the total value that it sees as being the accumulative Path Cost from all your equipment in this RSTP path.
To see the workings of how to control the used or preferred RSTP wlan interface then look in the bridge and at the ports of the bridge, you will notice that the tab STP most likely says Path Cost 10, by changing this value to a higher value then that port will be then the lower priority used port, so hereby one can force the LHGXL52ac to use the other wireless wlan.
Disadvantage of RSTP is the typical 5 seconds delay when it changes port, which is a problem for voip voice calls. If a link is 100% down say due to a power failure at one end of a radio link, then this works great, but if the wireless link has low signal level due to say mist or summer heat in the link path, then it will cause even more of a headache and require mostly manual intervention (by changing the cost value) at the time of the signal level drop off so that it does not keep toggling the traffic.

Bonding
Mikrotik Bonding (menu Interfaces, tab Bonding) has the advantage that it can move over to other interface in a split second therefore reducing hiccups or longer breaks in the connection so is the best method to use. Typical use would be a Mikrotik 2.9km or 1.8 mile wireless link RBLHG-60ad being a 60Ghz radio with a Mikrotik 5Ghz backup link (due to 60Ghz rain issues with this distance) and a 3rd Mikrotik router to do the bonding. With the bonding one can setup the changeover based on the packet loss, packet loss time, a wait time before reactivating the main 60Ghz link. This 3km link works great for us and should work fine within the one RBLHGG-5HPacD2HPnD-XL antenna as well.

Best of luck with it all Daniel

There are more than 2 ways @friesedraad...

As far as the Bonding you said, lets say you create a bonding on the 2 wlan interfaces, the primary link is up, there is a connection between the 2 antennas, but on the other side of the Link, the switch that the antenna is connected is off, or even someting happens between the connectivity of the antenna and the switch! The link will be UP but there will be no traffic flow and the bonding will never switch to the slave one... In case you configure ARP monitoring and ARP Target, this is not recommended unless a switch exists in between...

As for the RSTP it would be considered a better choice for me... Also except the path cost, which is actually the cost from the Antennas Point of view to our Root Bridge (We must be sure the Root Bridge elected is the Desired one, or we must manually set it) the port priority is advised to be configured as well...Port priority is set to ports facing away from the Root Bridge... So a combination of Path cost and Port priority would make it work...