It is happening to the rags right now. They've spent a shit load, brought in marquee players and a manager they thought would guarantee titles and 2 years into his tenure they're 13 points adrift at the halfway mark with a 6th place finish under their belt wondering how on earth they're going to close the gap.
Yes, but the question is whether they can unearth a good enough manager, to build them a team to compete & whether the Glazers are willing to keep allowing their bounty to be used on players.
City have raised the bar, imo to a level never before seen, & can still raise it still further, but imo not that much further. They are doing so many things right, as a team, that there is only so far it can go. You could find a Colin Bell to take over from Fern perhaps, a bigger faster Otamendi, a Harry Kane size cf who can also do what Aguero/Jesus do plus win a load of headers/shoot from distance, but imo we have almost reached a level which can't be surpassed, only equalled.
It's also a hell of a difficult standard to maintain & Barca couldn't do it. But if City did do it, then the question would be, whether other teams, such as the rags, could find a way (perhaps playing in a different style, but with loads of 'superstars' ) to match it. Mourinho has tried it by spoiling & lumping & it hasn't worked.
If they can't, & we maintain this standard, we consistently win. The other teams have to improve, even if we drop off a bit.
I imagine what will happen, is that some teams will learn & improve, enough to compete, & occasionally get on top, but we will still tend to be at the top more often than them, like with Barca & Bayern.
No guarantee the rags are one of those teams though.