Agreed. AC2 is elongated tutorial the game and the narrative is a step down from the philosophical aspirations of the first. To this day it's my least fav. game to actually play cause it doesn't let me free. Brotherhood was a large step up interms of freedom though.
You have it backwards, ACB started the annualisation, abhorrent pacing, Uncharted 2 style setpieces, exceedingly disjointed writing and overabundance of time wasting side content AC became a joke for. It's the game that introduced facebook time waiting management shit with the assassin recruits, ffs. And the reason it feels 'free' is because the main plot is a swiss cheese of stuff happening in a sequential order that shits game mechanics and side content on you as it rushes through introducing and reintroducing everything. Mechanical improvements aside, ACB is the blueprint for everything decent about AC1-2 becoming cynical and terrible.
AC2 on the other hand 'feels like an elongated tutorial' because it is has a firmer direction for the story, and the pacing of it and introduction of game mechanics is consistent with just enough room to breathe. You're so used to haphazard mess being the standard, ala ACB, ACR, AC3, etc, that it feels weird that a game actually gives a shit about the 20%-95% interim section of the game.
Though to be fair it loses a lot of steam once you get to Venice, routine sets in, and the secondary villains in the Pazzi are gone, while the main villain is being cockteased while also introing a different set of villains that you have no attachment to. Game has its issues, but everything bad about it is worse in ACB, while losing the good and turning the tolerable into intolerable. Novel elements in 2 that were just limited enough to not feel trashy padding like real estate, purchasing things, chests for a little extra gold, etc. are turned to 11 and become rancid. Even the inarguably 'better' elements, like UC style setpieces and Batman combat detract from it as a whole, the combat especially kills the game being about assassinating 1 dude and then hauling ass, which AC2 fucked a great deal already, and setpieces means you have to contrive scenarios for them.
tl;dr ACB is the harshest decline of the series