I think both cases 1 and 2 should fall under Messi-dependency. While it is normal to depend on your best players in some games, it is still called dependency. Think of Maradona and WC86 for example. When a team actively looks towards only 1 player to create chances and score goals when things are going wrong(like Barca last year), it's definitely called being dependent. It's not a bad thing, it's just something that we have to be careful with.
I should have been more specific.
Let me clarify - Messi being off still means he creates more chances than most elite players or scores a couple of goals. This was especially true last year and relates to the 3rd case I was talking about. A few of the games I had in mind where both Zaragoza games, Levante home, Bilbao home, Betis home, Racing away - in all of them, Messi scores at least 1 (mostly two) and usually has 1 assist. "Quite a few" might have been the wrong phrase to use, because looking back, Messi played well in an incredible number of matches. He got 24 MOTM in 37 games played.
Then there are games when everything goes wrong for him - like Chelsea both ties, Espanyol away, Getafe away, Madrid home, Osasuna away (although we lost that due to shambolic defending more than anything else). It's not a co-incidence that everytime this happens, we drop points. And it's not like we don't create chances in those games - we do - but they're not taken clinically, both by Messi and the other players.
Sure, in absolute terms, they might not be a lot of points, but in relation to how it affected the title race last year, they were pretty significant. Maybe I am overreacting - because after all, Madrid had a record breaking season last year. We finished 9! points behind Madrid yet ended up on 91 points which would've been enough to win the league in at least 90% of the years in Spanish La Liga history.
PS: In the Sevilla or Chelsea games, we spurned a lot of chances (not just Messi). It shouldn't have had to come down to a penalty in the 97th minute (Sevilla) or again a missed penalty (Chelsea).