If you're judging their success this season by luck then you should take a look at Liverpool's squad then you'll retrace your statement, if you're to judge next seasons Champions by squad depth then it would definitely be Liverpool they're a complete team and still thinking of adding more players to their depth, Crystal Palace might have been lucky last season but they shouldn't expect such luck this coming season.
I agree with you and I think Arsenal will have a very tough fight. Not only with Liverpool, but also with City! Just because Pep's team didn't absolutely dominate one season, everyone now thinks their dominant days are over. Manchester City are bringing in some new players and have also let some old ones go, they are currently rebuilding the team and will play and fight for the title next year just like Liverpool.