For those of us who started from ARR, we only had to do one expansion at a time and then we had 2 years of mostly doing content. You can actually play it the same way by stopping the MSQ after each expansion and doing all of the endgame content that was released in that expansion. That content all has a story as well but they are probably shorter than the the MSQ.

Each expansion has 12 8-person raids, a trial series consisting of 3 trials, a series of 3 alliance raids, a relic weapon grind which in Stormblood and Shadowbringers includes vast areas with interesting actions, bosses and raids. There are the deep dungeons Palace of the Dead or Heaven-on-High and 3 beast tribes for each expansion. There are a lot of sidequest dungeons up until Shadowbringers too. We also had other content released through these expansions, such as new triple triad NPCs to fight, blue mage updates, new games in the gold saucer and plenty of mount grinds from all of these things.