The squad is a work in progress all the time, it's never "sorted".
At the start of last season, Liverpool thought their defence/squad was sorted. Then VVD and Matip got injured. They needed their keeper to score a header to make the top 4, conceding in the process many goals and 6 consecutive losses at home (!). This fantasy of having an ideal squad is just that.
People tend to think linearly. They think that if you add Haaland to this squad, we will win everything without many problems. Football doesn't work like that, though. The better the squad, the more difficult it is to significantly improve it. If you add Haaland to Arsenal, the difference he will make for them will be huge, but if you add him to us, the difference will be much smaller than people think. Still, there will be some difference. The better you are, the more money you have to invest to make a small difference to the performances.
The law of diminishing returns holds in football as well. The difference in quality between a 30m player and a 100m player is much bigger than between a 100m player and a 200m player. To sign a better player than Mahrez you may need 100m in today's market. But to sign a much better player than Mahrez, you'll need 200m!
Liverpool fans, for instance, don't realize that the law of diminishing returns works in football. They think that if Klopp worked with City's budget, the difference for Liverpool would be dramatic. That's wrong, though, it's a mistake of the linear thinking.