I think the limiter would be the DM. There are tasks where others "helping" just isn't any help. You can spend all the actions you want, but you can't make me type any faster. On the other hand if you're half-way competent at English you could help my writing by being a proof-reader or copy-editor.
- Marty Lund
I appreciate this point. Certainly the DM always has a certain power to say no.
But lets take the english writing example. If we assume that no level of expertise is required to allow people to help, then under this premise anyone could help. So as long as "someone" is there, you have advantage. The reality of D&D is it is (primarily) a group activity, so invariably, someone who can aid you will be there.
So the "write an english document" example becomes a case of you are (in a game sense) always at advantage. When you have advantage 95% of the time, advantage isn't special, it doesn't have to be worked for, and its not gratifying when its achieved.
Also, under this assumption, as a DM, to say no, I would have to find reasons why not. I never like doing this. One of my MO's when DM'ing is "Find reasons to yes, not reasons to say no" (to me that is a very important one)...under a mechanic when the answer is always yes, you have nothing left but to find reasons for no. Leaves a funny taste in my mouth.