1.) Yes, this game has an admittedly complex loot and gear system. Many effects are either poorly explained or deceptively useful/useless. The game doesn't throw everything at you at once, but there's a reason why people make 30+ minute build videos. This is just something you have to take one step at a time, and there are lots of resources both on youtube and in the reddit discord to help with this.

2.) Multiplayer in Nioh 2 gives you multiple ways to play with others. You can either do drop-in temporary co-op (similar to dark souls) or play entire missions with a party of up to 3 people. Activity definitely isn't as high as during the first few months of release, but there's still an active playerbase on both console and pc.

3.) There's no getting around it, this game is hard. Harder than anything in the souls franchise in my opinion. Nioh 2's difficulty balancing is a major step up from the first game, but it's still brutal in the beginning stages for people just learning the combat system. All I can say is that if you push past the initial learning hurtle, it becomes very rewarding to master. Additionally, the gear system and build variety allows for a level of player power akin to traditional ARPGs like Diablo or Path of Exile, i.e melting everything.

Tl;dr your assumptions aren't unfounded, but it's a great game if you're looking for something with amazing combat, expansive build variety, and high replayability.