You didn't finish the game unless you saw credits roll. And after you watch the credits roll you did not finish the story.

If you don't want to finish the game that's fine. Do it however you like.

Rdr2 and rdr1 TOGETHER make one story.

It goes in this order.

Rdr2 then yes the rdr2 epilogue is actually still the game it is not over. It is not concluded. And then rdr1 is the end of the story. If you can't or don't want to play it I recommend watching the 4 hour YouTube video of the cut scenes so you can enjoy the story.

They put a lot of effort into this brilliant story and we should enjoy it.

Again if you don't want to fine, but the story is not just up to the epilogue.