We've not always struggled against teams that play defensively.
If we look at the past decade, I'd divide it into two main styles; the slow, possession-based style with a 3 man midfield and a counter-oriented double pivot system.
The former, which was the main style of Allegri, Pippo, Brocchi, Montella, Gattuso and Giampaolo, was very effective in home games against minnows who only showed up to defend. But it was easily exposed against competitive opponents who would press and aim for 3 points. This lead to a lot of poor results in away games against teams in the bottom half.
The latter was/is used by Seedorf, Mihajlovic and Pioli. It's more direct and better prepared for competitive games.
Not so much for matches against opponents that aren't leaving any opportunities to counterattack.
However there are ways to combine. I'm aware that it has not been this black and white.
I think Pioli has been getting closer than any of our previous coaches in finding that perfect balance. We're playing with a lot more possession since the switch to 4-2-3-1. The team is doing more than just counter-attacks. Players like Hakan, Bona and a versatile, targetman like Ibra have reduced the problem. There have been lots of great 1-2s and patient, slow buildups in the final third.
I wouldn't pin all those disappointing results on difficulties with breaking down teams though.
The Lecce game was his first game in charge, and he was let down by wasteful players like this season's Piatek and Paqueta.
The Fiorentina game was more of a fatigue issue I think.
The team was out of energy, but there was no Rebic or Hakan on the bench who could re-energize us the way they've been doing in these last two games and in January. All of our energetic players started that game, and this was also the case in other February games with strong first halves and weak second halves, such as the derby. The lesson to learn from that month is that we need offensive impact subs. Pioli doesn't have any when he fields our strongest XI. Saelemaekers has energy, but he seems to have less end product than Borini. Leao has end product, but not much energy.
As for the other poor big game results, they were among his first games. Fans weren't even disappointed at the time because the performances weren't bad. We created as many if not more chances than Juve, Roma, Napoli and Lazio. However Theo seemed to be the only one who could take his chances.
That has changed. He's had more time with the squad, more time finding solutions to the countless number of problems he inherited from Giampaolo. He now has Rebic, who makes a lot of technical errors, but he can run and he can score. He has Bona, who returned from yet another injury and can't run anymore, but he can still score. He has Ibra, who despite his age and flaws isn't completely useless like this season's Piatek. Pioli faced Roma, Lazio and Juve in a better position this time, and defeated all 3 of them. We have faced Juve 3 times since that November game and not lost any of them.
Yeah, he lost 5-0 to Atalanta, with Calabria as LB and the Suso-attack, but he's also the same coach who destroyed Gasperini's Atalanta, 7-1 with fodders like Gary Medel at Inter. That was the same Atalanta side that finished 4th with Kessie and pre-injuries Caldara and Conti. He also had a 7-1 victory with his mediocre Fiorentina side against Roma last season.