Coach will indeed be the first party who is always blamed when the team being coached experiences failure or significant decline in performance, conditions like this are experienced by all existing team and those who always experience decline are definitely coaches who are always considered bad in their performance.
Regarding Bayern Munich, I think Tuchel is still working well because they can still fight until now they are in the quarter-finals, if the decline occurs significantly and they are categorized as weak team then they will have been eliminated from the start.
UCL competition is the most prestigious competition and any European team definitely wants to be able to win the UCL title, this season Tuchel targets to bring Bayern Munich to win the UCL.
From here, I think it is still normal for Bayern Munich to experience decline in performance in the Bundesliga competition as long as in important competitions like the UCL they are still strong team.
Moreover, Bayern Munich is the most successful team in winning the Bundesliga title, so if this season fails then it is not failure that should be disappointed.
They can still stay in second place and have the chance to become runners-up this season.
Tuchel's presence in the team ought to make a significant impact to their endeavors all time and also Kane's performance needed to add a big advantage to them but so far, their recent games have turned out opposite of their normal and expected performance rate. It'll only mean that their journey this season to a top spot is threatened and no one can say exactly if they'll be able to scale through it.
They've not been encouraging and it's quite appaling that they remain depreciated week after week. Sadly though, Tuchel's stay in the club is seemingly threatened, his days are actually numbered and it's understandable that the management would want a switch for the coach position as they expected him to be better considering how much effort his put in recent times and even with flaws, they need not to keep overlooking it as it's unending.
Well it'll only task them to find a proper hand that'll replace Tuchel's as so far they need not to take their chances and cause this to continue unto the next season. Alonso is being quested for and if they're able to secure him, well, hopefully he'll be able to take them out of the state they are. His records are speaking for him and so it's understandable that they see him as a proper prospect for the job ahead in the club.
Not also forgetting the fact that they've got to strive to gain back their name in the league. Yes, acquiring new players is essential to a team and with their caliber, they really have what it takes to go for the best of the bests. This season's experience should be enough for them to learn and react better to next season. They're an impactful team and so they should do their best to get whatever necessities needed for a good team outcome.