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This is not the first Chelsea gave a long contract duration, before that Chelsea also gave 5 years contract duration to Graham Potter, but Chelsea sacked him even though he wasn't reach a year. So, Chelsea can sack him whenever they want.
It's a mistake for Chelsea to sack Pochettino and hire Maresca, did they not see Maresca was the one who make Palma Calcio 1913 relegated from Serie A to Serie B? perhaps this is what Chelsea wants, they want Chelsea to relegated from Premier League.
I admit that I am a Chelsea fan, but I see that Boehly is an owner who is difficult to trust, it is clear from what he did to Potter and Pochettino, he really is not a patient owner. This is the first time I heard about Maresca and even though she had a bad experience as you said, Chelsea have good players, I'm sure Maresca will be able to work well with the Chelsea squad and management, especially since the issue is that Maresca is a former pupil of Pep Guardiola, so Let's just give Maresca the opportunity to work with Chelsea.