I disagree. The message is clear that reality is messy. But not that love is an illusion. Those two messages aren't hand in hand. In the time stop episode he explicitly sacrifices himself for love and reflects on that. Most Ricks don't seem to love their grandkids but the main Rick does. This has been a plot point since season 1.
I think Rick was frequently wrong even in early material. He was wrong about the planet being ruled by advanced males that lost the need for females. He was wrong about his relationship with Unity and nearly kills himself for it. He was wrong when he destroyed his own universe. Rick lives in a meaningless world because he's vastly surpassed its limitations. But he's not better for it.
Most plot arcs take an existing concept, writing tactic, plot, or trope, and deconstruct its assumptions to then reconstruct the juicy bits. Like the Purge episode. Rick is too powerful to be bothered by the purge. Gets bored. But ends on gleeful gratuitous violence because its kind of fun. Which gets back to what I would say is the central message of the show. Even if the world is dumb/messy/nihilistic/bad; it can still be awesome. Things can be good without a need for them to be intrinsically good.
I think this is one of the more pressing artistic idea of our times. Same for Everything Everywhere All At Once.