Landscape system is something to work around or adjust and profile(!) much if u work on a big environment.
U could look at solutions like ShaderWorld or WorldScape but you will miss out on RVT and will need
GPU dedicated servers for SW if u are looking at Multiplayer Open World.
As MostHost_LA pointed out more above, those are all good tips, since there is not an easy way out.
What we did in a few ( mostly smaller ) environments is measure differences all the time,
using ( Nanite ) Meshes is possible, even more when using HISM to keep Drawcalls low.
Nanite could open doors, but size of Nanite Meshes can be tricky and u probably will
need to (import) Baked VP, it might be a kind of solution depending on the project.
As for (costly) Collisions, u could add a very low Lod (1 to 10% depending on the Mesh)
and let Nanite use that Lod as a “cheap” Collision if u dont have one (Blender etc).
I can not emphasize enough that profiling is what u need in UE, in every aspect of it,
many small gains make one bigger gain in the end, surely in big projects.
Curious if they introduce (this) Landscape system with Nanite, it would be massive in size i guess.
Either way, UE is profiling all the time, there is no away around it. it’s a good Engine (imo),
but a heavy and frustrating one, people look at YT clips and think they can be a dev out of the box
but that’s not the case, UE is very complex and insane much work if u aspire visual
quality in harmony with performance, especially for Multiplayer & Open World games.
Still upto today cpp is the way to go in UE for big projects,
u compensate much that way so u “could” keep the Landscape system cost.