Arma Is it possible to have an open world game without a main story/questline?

Got me thinking after a recent play through of Watch Dogs and the main story just seemed to get in the way of the other more compelling activities. I think now we're seeing more and more games become RPG-Lite but with established protagonist and a quest to pursue. Can't we do away with that? If anything I think RDR2 might support this as well, and games like Stardew Valley.

For me it's a question of pursuit and choice. If we take Watch Dogs as the consistent example, the fun parts for me were the investigations, fixers, hideouts, intrusions, dynamic crime (to an extent). These are considered 'filler' I guess (in open world games), same as monster nests, bandit camps in TW3. For me it's easier to role play and feel engaged if I am choosing which activity to do.

The problem lies in that the 'filler' tasks are often not fun, very linear and just used as an XP boost or loot drop. Imagine just being able to walk round an open world, do the regular everyday activities and choose your own stories or activities to take an interest in. Maybe you stop in a town and stay in a hotel and meet an interesting friendly NPC, you can then maybe stay in touch and a random event might happen like they got burgled/attacked and send a message. You can choose to send them money, seek vengeance etc.

I know all those are difficult to produce but ultimately do we need a main questline, if the world and things you can do are compelling enough and designed so the player can pursue what they want?