The biggest thing to remember with mesh, is the individual units have to have connection to each other. If you have a mesh node that is way out by itself and can not connect to any of the other mesh nodes, it is useless - dead.

So you end of with an area blanketed with the nodes. And each node is a low powered WAP for that area it is in.
Think 'leap frogging', only it is called 'hops' back to the point of origin.

If you are dealing with a large area and some of the coverage is very far away (over 100 meters), then point to point wireless with another WAP attached to that is the best (and cost effective) direction.
Relying on a mesh network for something that far away, would probably require 4-5 devices between the areas. Now if you need coverage throughout those areas, then no big deal. But I would still be concerned with the furthest areas and the 4-5 hops they would have to make to get service.

What Ubiquiti unit did you use? I have the UAP-AC-M-PRO installed outdoors for almost 2 years now and no problems. Sees temps from +30C to -35C and is in direct contact with weather (wind, rain, snow, ice).

This unit provides at least 600' of coverage and they can be installed on a Mesh network (my installation is not utilizing the Mesh).

The only Unifi units that are designed to be installed in direct weather are their AC-M units. Their AC units can be installed outside but are designed for indirect contact with rain and snow (under soffit, gazebo roof, etc.). The AirFiber and AirMax lines are designed for outdoor use however are more designed for P2P not as a WAP.