AS Roma just parted ways with their coach and now they will work with a new coach who in my opinion is a less successful coach, so I am not too sure about the new AS Roma coach.
Manchester United is an inconsistent team, several times they showed their weaknesses, yes they are good in the game and for the next game they can't show anything good. Some people say that the main problem lies with the coach, and I am one of those who think like that.
Tottenham is a good team, but they are not a champion team. I mean they are just good but not strong enough to win the title. I don't think they are bad, but that's what I see from them in all competitions, especially in the English league.
Roma management repeating their mistakes which they have done in past and ruin the club's development with De Rossie surely deserve some more time, but they sacked him and bring a mediocre coach which is having not good past and most chances he can't bring positive results in near future as well because things are never been easy to handle club at this stage and bring quick better results specially while you are having the toughest challengers in UEFA Europa Cup title race.
With this change most chances they are not going to have better results because Roma is surely big club, and they needed good time for setting things which are surely not easy for the new coach.
Even though those teams you mentioned haven't really done anything convincing in their domestic leagues but they can still do better in Europa league. Manchester United is one of the teams that also has a fair record in the Europa league so if Ten Haag can take the Europa league games seriously and ensure that they don't lose more matches than win. However, the bigger teams from top European leagues should make sure they improve in their performances because it will be bad if they don't advance after the group stage matches but I believe they will try their best.
We can't currently predict about any team with we are having just few rounds in domestic leagues and things are going not favourable to predict about who is going to be favourite for the title race Manchester United is surely good club, but their nature is not predictable and few other clubs are also having same issues into their domestic leagues which are making things difficult to talk about winner even few clubs are having enough sources to go through, but their priorities are also never been understandable with mostly clubs love to have better results in domestic league instead of having better result in UEFA Europa Cup.