My group can get a game of 4th edition finished in four to five hours. We are seasoned players, though. Twilight Imperium is both a strategically and tactically rich 4X game, which is why it's one of my favorites.
That said, I am not opposed to long games. I recently played Fire in the Sky, which took me and my opponent 4 four-hour sessions to complete.
I look at it as no different than a campaign game such as Gloomhaven. Gloomhaven took my group two years to finish.
Dune (either the original AH edition or the 2019 GF9 edition)
Battletech
Descent (first edition)
Mage Wars Arena
Battlestar Galactica
Food Chain Magnate
Scythe
Blood Bowl
Twilight Imperium (fourth edition)
War of the Ring (second edition)
Millenium Blades
Exceed
BattleCON
Cosmic Encounter
Sidereal Confluence
Sekigahara
Triumph & Tragedy
Iron Ships & Wooden Men
Cloudspire
Forbidden Stars
Go