They aren't playing any differently, same tactical decisions as under Tito and since the start of the season. People are just figuring out how to play against them, in part, the other part is Puyol's form has been pretty terrible, and Messi has finally had some useless games, and in doing so, everyone else's on going issues are shown up. Pedro hasn't been in good form for basically 2 years, Villa barely gets a game, Iniesta misses most of his shots and Messi stays FAR to deep for the main striker.
Barca haven't changed in the past two months, their one dimensional tactics and style of the past 18 months is simply so predictable teams are finally adapting to them.
No one here knows how involved Tito was BEFORE his cancer or since. Some managers take every training session and every motivational speech, some do neither, a manager isn't a specific job, its a role that most managers do differently. Wenger by all accounts won't let Bould train the defence as Bould see's fit, other managers barely take any training sessions.
As for people saying anyone can manage a great team, it should be quantified as most people say anyone who doesn't do completely stupid crap, can manage a top team pretty easily, keep the ball rolling is a large part of the job when you take over a successful team, that isn't the same as saying a crap manager can manage a great team and still be successful.
The fact is Barcelona may have had some absurd results and a great run of form in terms of winning, but at the same stage last year they had 12 clean sheets in the league already, this year they have 5. The results are one thing, but they have frequently gone behind this year, they have frequently had late goals to win games, they've had less thrashings of teams, they've been closer to a bunch of losses this year, even if they snatched the win at the end, than last year.
Their overall performances have frequently been worse, despite getting the wins, they've failed to dominate more games and let comparitively worse teams give them more trouble.
They've got more points, but they've played worse football for HUGE spells of games than they did last year, and most definitely the year before.
So Tito, the football hasn't changed in the past 2 months, just the results, the theory that anyone at all can manage, no, the theory has always basically been that winning at Barca doesn't automatically make you a great manager. I think if you look at the Guardiola "is he good" thread, the general opinions were either, he's the best ever, or he took over the best club, he MIGHT be great, he's not proven it, it takes less to take over Barca and win a title than to take over Athletico and win the title.
Compared to last year Barca have conceded 28 goals vs 18 at the same point(roughly) in the season, noticeably worse, they've scored less at home but WAY more away, away last year was where they sucked, 45 goals home and 20 away, this years its 42 and 40, massive massive difference away from home.
They've been worse as a team, and worse defensively but also found their scoring boots away from home.
Except for Messi and his ridiculous scoring record, I don't think there is another Barca player who has played at the same level they did last year.