Yes, I agree. But Koeman's setup (allowing De Jong to basically wait for chances to run upfront with little involvement) changes drastically when Busquets is out. Busquets is the one progressing the ball and thus Pedri receives it in advances positions compared to Puig. Puig does position himself well, but it's way easier to do around the centre than where Pedri's doing it. It doesn't suit Pedri either, as he looked much better with more space in the beginning of the season.
In my opinion, it's no wonder we look more shaky at the back with Puig on the field because even though his actions look nicer, they allow the opponent more time on the ball. And the setup with Pique and Lenglet at the back can't have it.
Of course, a faster build-up will generate more chances for you, but also more errors. That's the tradeoff. But I'd rather have that. The alternative is having the same slow-ass boring build-up like before, hoping that maybe the CBs won't have to deal with a higher tempo. The reality is Koeman is slowly messing up and going back to the same old football we saw in previous years. Step by step the idea of a rebuild is being lost.
Busquets moving the ball is a no-go. Way too slow. Only technique, at a snail's pace, doesn't cut it anymore. Just take him out and replace him with De Jong. See how we do. Have someone cover his spot when he goes go up.
Take an example from how Casemiro joins the offense at Madrid in many moments. Some Madrid player will cover that area temporarily. Either a fullback, either one of the two interiors, depending on the situation. It's a myth that a DM can't join offense at moments. You just have to make a plan for it to happen in a controlled manner.
At Barca in most home games from La Liga, the high-line CBs are the ones who should stand in the DM position anyway. That's what happens at most big teams when playing vs much inferior sides.