Not necessarily, they were playing a very similar team with no injuries, they had amazing form. A summer off can completely break the form of such a run so it's not too surprising.
Hull on the other hand have what is incidentally exactly that, because of so many injuries this team has played basically every game so far, no chance to build up an entire squad slowly, so this team is fitter than probably most other squads and had a chance to gain that "play every game with same squad" form. Of course, a couple of injuries would be a huge issue for them and it would be very very easy for Hull to be one of the most tired squads come the end of the season.
I suspect that Leicester will struggle to transition into a squad that can produce form with a team that changes much more often, but that is to be expected. That is why the top 4 particularly but the top 6-7 is hard to break into consistently because you get europe and have to become a team that can rest 4 players and still play well. Leicester actually have decent money, decent backing and are buying decent players. I can see them yoyo-ing up and down from top 6 to 7-11th for a few seasons as they establish themselves before maybe getting higher up more consistently. What I hope for them is a good CL campaign and a non awful league campaign. I think they'll improve significantly over the year but struggle to find their form in the league for a while at first.