I never got the impression that Shen Wei did not want ZYL to participate at all in the fight against Ye Zun, rather that he thought ZYL should handle things in Haixing (still plenty dangerous) and that he needed to handle the Dixing side of things and his brother (who he probably felt particularly responsible for).

I agree with this. He never tries to keep ZYL out of things entirely. But there are some tasks he definitely sees as his - and with justification, because what can a normal human do against Ye Zun? (ZYL does tries absolutely everything he can think of, towards the end! Including using the Awl! And to no avail.)