I advise you watch a game of T1 when they are in sping 2025 and a game of T1 at world, it's the most insane scaling I've ever seen

sometimes teams improve, sometimes they get worse

Meta changes throughout the year and teams overall obviously improve, rosters that have new players also need to get used to playing with eachother. Sometimes the improvement is just slower than other teams so it looks like they may stagnate over the year.