To think that running aimlessly round a field has no benefits

[Unintentionallycausingoffence]

Some family members have suggested taking DS to run round a field while the adults stand around chatting as a source of entertainment or a trip out. AIBU in thinking there are far more stimulating and interesting activities?. Having structure to running is better but they mean just running around

What's wrong with that? I used to take my son out to the countryside/open spaces. He'd kick a ball around or fly a kite if we had one, or just use his imagination and "play". We'd usually take a picnic or maybe just some hot drinks and a few folding chairs.

I honestly don't think kids know how to play anymore. It's got to be a theme park or nothing. It'll do him good.

This.

From what you put in your first post, YA obviously BVU.

Now, depending on your dc's very specific needs, it might or might not be something he can cope with, we don't know him. Presumably, whoever suggested this wasn't aware that this would, in your view, be unsuitable for him.
Perhaps explain to them why you think it won't work, and either people can come up with mitigations, or people might be willing to go to one of your alternative suggestions. Talk to them and see.

I have since sort advice on safe places and safe ways to do this, which I’m going to try. Including stimulating and activities is probably a good idea. DS school schedules a lot of safe outdoor play into their daily timetable