Man City will undoubtedly be strong again. They aren't losing anyone of consequence and if they sign Kane, you might as well just go ahead and give them the trophy again. They are quickly becoming what United was back in the 90s and 00s.
Chelsea got a huge boost switching managers. They still have some roster issues though. I'm not sold they can mount a title challenge without an actual striker.
Liverpool and Man United are both in the same boat, IMO. They both have some requirements that need to be addressed in the transfer market. Getting Van Dijk would be a boost but wouldn't solve the fundamental problem of a squad lacking depth. And there are questions about Mane and Salah even staying with the club. United absolutely need at least 3 quality additions. They've got to get an elite center/holding mid so we can get rid of McFred once and for all. If they don't address that, then they won't be legitimate challengers...even if they sign Kane.