Separate from whether the penalty sliders are powerful enough or not - across all regular season and postseason games in 2021,
NFL teams each committed 1.19 offensive holding penalties per game (accepted or declined).
Given your anecdotal reports compared to actual NFL data: 0, 1, or 2 offensive holding fouls per team per Madden game should be an acceptable number on default settings.
How many such fouls should occur with the offensive holding slider maxed out? Admittedly that is another story entirely. I would honestly expect to see a dozen or so total calls with the slider at 99. I recall in Madden 16 when the penalty sliders were all maxed out you couldn’t go more than three plays without a foul lol.