Proper Map making guide

Here is the thing …
Ark uses level streaming, but, on a very very simple level. Yes they use “chunks” like level streaming, but, all levels are always loaded. They do not cull out. Your performance issue is possibly something other then the landscape itself (depending on the map res, 1k, 2k, 4k, 8k)
Ark uses 4.5.1 with some 4.7 features
Ark uses some really out of date assets
Ark uses some REALLY bad blueprint code, like, really bad
Ark uses little to no optimization in any area of the code/blueprinting
Ark uses 0 documentation (for its modders) and most, if not all, data is so far out of date its nearly worthless

^ we can argue that the functionality and issues are due to being so far out of date, and, using an edited version (to work for them) of the 4.5.1 source for UE4, the world will never know. Point is, you are doomed from day 1.

The foliage scheme > you are correct. Nothing more then a culling reason. Its setup wrong, for proper foliage culling, but, F it … its their design
I made a map, using the proper culling and design schemes and i was able to extend to replication bounds (1.2 mil x -1.2 mil X Y) and you would have never known things were culled out at any time. The trees just use LOD and stay in place (to cover that all the other foliage is missing). Its just a performance trick is all. Hide what users cant see from a distance to help unload and save on memory.

Making 100 maps and adding them, or, 1 map and using it, makes no real difference. I say this while biting my tongue due to its situational. I wouldnt ever load a 4k map in Ark, thats just asking for pain. 1k sure, anything less, might get a bit ugly on the eyes. Welcome to making maps - you think its bad in the first day, just give it time, it will get much worse. lol.