I think Starcraft II makes a good example of this. I played mostly Wings of Liberty and a little bit of Heart of the Swarm, but the single player campaign you get all the classic units plus a bunch of new ones and there's a bunch of permanent upgrades you earn throughout the campaign, like being able to pod drop barrack units anywhere on the map.
Then you switch to multiplayer and like half the units are cut out and the entire unique campaign upgrade tree is gone. But Blizzard is/was masters at this balancing game and no exactly what they're doing, building a tighter package for the multiplayer by cutting the excess.
So while I know there's a scene of people that are into it I've always wondered how viable Age of Empires is as a multiplayer focused game vs single player. As a 'historical' game, there are a lot of components making it a bit closer to a single player game like Civ which is great for single player but may not necessarily be optimally streamlined for multiplayer. Speaking of the Civilization series, there you do have a multiplayer option that some people do but most play single player. Where as with Starcraft the player base leans more heavily towards the multiplayer. I'm curious what the actual balance is for the Age of Series.
Also going off topic but speaking of all this I'm really excited what Microsoft has in store for us with their brand new 4X/Grand Strategy Game in development,
Ara: History Untold. I'm kind of burned out on Civ VI but while there's been a few attempts in recent years no one's been able to unseat them.