What you have described is exactly the premise of buying a game that is in development or early access. You wouldn't buy an early access title on Steam, expecting to then pay again when it is fully released, would you?
As a real life example, I present you Wayfinders. A game that came out in paid early access as a shared space mmorpg (think Destiny or Diablo 4) that was an always online title slated to have battle passes, seasons, etc, as a live service title. The game developers didn't like the way the game was going and broke away from their publisher and completely remade the game again, removing all the live service and always online parts, and rebalancing and reworking everything. They even had to remove it from Steam for roughly a year. When it came back, in your terms, it woas "not exactly the same game". It was even renamed to Wayfinder Echoes. Even after all that, the ones who bought it before didn't have to pay another cent, and even got extra bonuses in game such as an early character unlock and boosted currency, all for supporting them throughout. That is what gratitude looks like
I'm not saying you have to do anything that big, but asking people who have bnought the game already to buy it again just because you putr more development into a game that was in development is a bit of a low blow and a middle finger to those who have paid, regardless of how much they paid.