Would a Park tool Pin spanner be easier to use on a Mavic wheel than the tool that comes with it. I find the tool very difficult to hold in place and it always slips.

Like you I found the plastic tool poor. Purchased a better tool and much easier.
Wheels since gone so don’t use the tool.

It’s meant to slip so that you can’t over tighten it.

I always find a pair of circlip pliers best for the job and I can’t get the Mavic tool on the nut while the wheel is mounted anyway.