I bothered to go look it up, I've got 1200 hours of PvE activities, most of which will be matchmade activities. 400 hours in the crucible, the vast majority of those are with me queuing with friends (which is another exciting discussion on SBMM and Lobby Balance).
At a rough guess, I'd say I'd spend a good 20% of my time truly solo doing bounties and roaming the world working on quests and the like, which include activities like public events, escalation protocol and the Contact public event which all require other people in the game world (I've duo'd Contact with randoms and farmed level 7 EP bosses with a friend), the next 20% solo queuing for matchmaking activities like strikes, hero level Ordeals, menagerie and forges.
The rest of the time, I'm either duo'd or with a fireteam doing Master Ordeals, PvPing, Dungeons or harder quest lines like Zero Hour. After that.. I'm in the D2 PC LFG discord, finding teams to do Pit of Heresy and Prophecy on the weekly, or raids. I don't do raids that often, but with a bunch of things going away, I started doing all the raids, some of which I've never done before, like Spire of Stars.
Nightfall: Ordeal at hero level (the highest/hardest/best rewards that you can matchmake for) matchmade activity is a sterling example of why and how matchmade activities are loaded with lazy, uninformed and frankly careless people. They just hit matchmake and expect to get carried. I don't think that's entirely those players fault either.
I've done Ordeals a fair bit, while a normal strike is able to be brute forced, the Ordeal requires a little more planning on weapon/ability selection. After doing a bunch of these solo queued I realised the ONLY way I was going to finish the Ordeal in under 30 minutes was to treat the other 2 people in the party as if they weren't there. Meaning I needed to bring all the weapon types to beat all of the champions, and all the right damage types to deal with the shields. This means I don't have to rely on someone else being able to break the shield on a barrier champion, or deal with that Unstoppable Ogre, or drop that Arc shield on the Hive Knights.
Edit: So there's a fuckload of content that can be done in small blocks. 90% of all content is like that. However, if you want to do raids or Master or Grandmaster Nightfalls, then yeah, get some friends, or start using the LFG Discord.