AO is an expensive effect, so of course it's not supported in LWRP.
It sounds like you aren't baking your textures. Generally it's not a good idea to import material settings directly from Blender:
- Some settings can't be imported, so your material often will look different in Unity. Blender is primarily designed for pre-rendered graphics, while Unity is designed for real-time graphics. This means that Blender has all kinds of texture and lighting settings that have no equivalent in Unity.
- You often end up with one mesh that uses 5 - 10 different materials, which makes the mesh more expensive to render
- After importing enough models, your project will get filled with an overwhelming number of imported materials, making it nearly impossible to find a specific material with the search bar.
Texture baking refers to creating a UV-mapped texture from the material and lighting settings that you have configured in your 3D modeling software (Blender in this case). This is the only way you're going to be able to recreate the look of AO without an expensive post-process shader. Gradients, patterns, AO, etc can all be baked into a single albedo/diffuse texture, which is inexpensive to render. If necessary, you can also bake specular, normal maps, etc.
Texture baking is an essential skill for any 3D artist working with a game engine. If you don't know how to bake textures, you should learn this immediately: https://docs.blender.org/manual/en/latest/render/cycles/baking.html