Blender 2.8 and Cycles were behaving normally with thousands of splines but something changed these last months – I don’t know when – which makes Cycles unusable.
To test that, it’s pretty simple:
- Take the latest beta 2.8
- Create roughly 10’000 splines with 10 random points each within one curve object with a script (note that you only have one curve object with many splines in it so this is usually fast)
- Bevel the curve object so that the splines are meshed
- Set render engine to Cycles and hit preview
You’re in for an extremely long and unbearable wait.
In comparison, Eevee behaves normally and is usable, just like Cycles used to be.
Does somebody (Brecht?) know about that?