i can give you facts that in 90% off the games my starters play between 34 and 38 minutes. 32 and 33 or more than 38 min happens, but very rarely. off course depending on circumstances like fouls, injuries etc it can differ more. but i play SFDC in 99% off my games and my starters in 90% or higher % always have between 34 and 38 min
And like koz said, it's not universally true. I actually found your claim so surprising based on my own experiences that I went through my own competitive and PL games this season. I checked for each game whether at least 3 of the 5 starters played between 34 and 38 minutes. Here is a summary of my findings:
In 11 games, at least 3 starters had 34-38 minutes.
In 18 games, this was not the case.
That's about 38%, which is way below your findings.
In addition to the games listed above, 1 game went to OT and 1 game went to double-OT. In these two games, most starters played more than 40 minutes, but that is hardly surprising. I would also like to note that out of the 29 games that did not go to OT, there were several games where all my starters were between 34 and 38 minutes, and several games were none my starters were between 34 and 38 minutes. Obviously, in all games I used strictly follow depth chart. In addition, in most games I let the players play in foul trouble.