Am I wrong or mehrunes razor has no .bsa? I'm just making a huge archive of the dlcs and I'm wondering if my eyesight fails me, or mehrunes just use oblivion asset and so the .bsa isn't needed.

Your eyes aren't failing - that one just has an ESP.

Thanks for help. I've got another question. Right now I've installed spell tomes. How come the installer is around 2 mb, but the .esp is infinitely more little than that?

I've no idea, but you're right - it's only got a tiny ESP and nothing else.

Thanks for help.