I think that's about the size of it. This seems like a "bad deal" to restaurants because they aren't really thinking of the problem correctly. Restaurants view having to sell a meal via GrubHub as selling a discounted meal, because the customer pays menu price but the delivery service charges a fee. So the restaurant makes less cash than they would to serve the same food to a table.
And the reason they think this is that when customers used to order "takeout", they'd still pay full price and the restaurant would keep all of it. So it feels like they've lost something.
But that's all wrong, because takeout used to be "improperly" (per a market analysis) marked up. Serving takeout is cheaper: no need for tables and dishes and servers. Lots of restaurants have known this forever and prioritized their takeout business, and done very well.
But now those savings are all being eaten up by another party that is providing useful improved services to the customer, and restaurants don't like it. Well... I guess I wouldn't either, but what they're complaining about isn't so much unfair competition than it is (heh) the elimination of what for them used to be a free lunch.
The market will re-equilibrate. It always does. But yeah, until it does the distribution of changes will not be fair. It never is.