The key is that nothing is certain: City/Liverpool may win all their games, but it's not highly likely (say 75%). It's more likely that City win all their games in comparison to Liverpool, but it's not guaranteed. And there is no recipe to win all games, for football involves luck (and VAR...).
The "if Liverpool/City win this game, then this will happen" takes are a bit naive, imo. Try to think in probabilities instead of relying on vague and unreliable intuitions. And take context into account: don't think of the difficulty of games in isolation, but try to factor in physical and mental fatigue from previous games. For instance, given that Liverpool's games vs Villa and Southampton come after a series of games, including games vs Spurs and Chelsea respectively, they may be more difficult than if considered out of context.
It's possible that Liverpool win everything, but it's quite unlikely (1/10). City have roughly 2.5 times better chance to win the double than Liverpool the quadruple. Everything is possible, some outcomes are significantly more likely than other outcomes, though.
Now, intuitions may be reliable at times. Personally, I have sometimes pretty strong intuitions, and they come true. But such intuitions (e.g., that Jesus will finish the season strongly, wrote about this already in March) are based on rational expectations (calculations), they are more rational than it may seem.