A temporary solution is better than none or some for which you then have to pay a lot of money (termination of the contract).
There are rumors that Nagelsmann will lead the team in the summer, and now he wants to rest until the end of the season (or just does not want to get under the Real Madrid ice rink). But there are also rumors that PSG also want to sign Nagelsmann. Will he, like Mbappe, negotiate for himself the best conditions from two rich clubs? Cunningly!
It's crystal clear that Chelsea needs a manager that can turn the fortunes of the club around, wether temporary or permanent but I don't think that Frank Lampard is the best available man for the job. Julian Nagelsmann would've been a better option or they would've gone for Zinedine Zidane or any other high profile Manager that's available but they went for Lampard that was easy to approach and negotiate with. Todd Boehly got it wrong by sacking Thomas Tuchel last year and he'll always regret that decision till when he get a better replacement
Let's see how it all ends up in the end. Maybe City will go to the Championship, Guardiola will be sacked and Chelsea will intercept him

Or Chelsea can somehow convince Zidane to move to the Premier League (no less fantastic). At the moment we don't know Chelsea's goals so we can't fully assess their actions.
As for Tuchel, I think Boehly will never remember him - for him it's just business. If the employees do not give results, he changes them. Someday the kaleidoscope will form into the correct picture.
Guardiola knows his way to winning the Champions League but this time they are going to face Bayern Munich and there is Tuchel coaching that team who is experienced in the champions league hiring Tuchle was a wise move for Bayern Mucnich to play against Manchester City with better shape than before. However, this can be very hard to predict for anyone.