I think most people prefer thin lube for offstring. Since the string isn’t wrapped around the axle, adding more resistance in the bearing won’t help wind the string back up as much when you are playing offstring as it normally would. You still have to use a bind to get the string to wrap around and catch on the response system/walls of the yoyo to get it to return. Even if the string wraps around the bearing, if it never catches on the sides of the yoyo, it is likely to just slip off.
Because of that, offstring yoyos usually make returns easier by making the gap smaller rather than relying on lube for response. Using a small gap and thin lube will let you get good spin time with easy returns, while a wider gap yoyo with thick lube will probably still be harder to return. It would probably help a little, but I think most players see a smaller gap as a better trade-off for offstring than a more responsive bearing, and the smaller gap is usually enough on its own.