If we go position by position, SF is usually strong all time. But now, SF is kinda relatively weaker.
The best SFs in the game are:
Jaylen Brown, Butler, Lauri, Derozan, Ingram, etc
WHERE IS LEBRON/TATUM/KD/KAWHI?
They are now Power Forwards. They strengthen the PF spot. But left the SF weaker.
Ofc, I know some people will argue things like
“SF and PF are basically both Wings or Swings (Small Wing and Tall Wing)”
““There is no SF and PF now. Only Forwards””
But still , technically the Best SFs now is converted into PF for some reason.
Leaving Brown as the only Top 15 player in SF spot.
To answer OPs question: this happens quite a bit. Aging player in KD, Kawhi, and LeBron get slower, less athletic while developing “traditional” post moves in later life. That, coupled with the small ball meta of today’s NBA, would obviously shift them over to the 4.