Not just those two.
Lewandowski, while still being class, is not at his peak anymore. Müller could change jobs with the mascot and the team wouldn't loose much. Boateng, Javi and Alaba all played better in the past as well. I can't even bring myself to complain about Thiago, because he is one of the better players over the course of the last two years. Coman, who was genuinely exciting, is getting destroyed by injuries.
There have been talks about bringing in a new generation of players since the second season of Pep, but it never really worked for various reasons. Now the old guard is getting really old or left already, but there are not enough players ready and able to step up. Kimmich and Süle are the only two who I trust to do so.
Many caf-bayern fans complaint over the last two years that the team is decling a lot, but the lack of competition in the Bundesliga was hiding it to some extend.
Hiring Kovacs is just the last of many errors. He deserves to get sacked because he is doing a terrible job, but he is not sole responsible for this mess.
In a way he is Bayern's Moyes: not good enough but the rot goes deeper.