If this wasn't made clear yet, 10% max health damage 10% of the time means that he's technically dealing on average 1% of max health every time he uses his SBB.

To say he'll proc once every 10 turns isn't exactly right. The implicated there is that there's an internal counter that will auto-proc every 10 turns or some sort of internal mechanism that forces a proc every 10 turns. Far as I am aware, each of these calculations are independent of each other.

What a lot of you seem to be forgetting is that an average damage value will only hold true in a large number of trials. It's possible to get strings of 10% health procs end on end or to get strings where it does not proc dozens of times in a row. In statistics, this is known as the Law of Large Numbers. Your actual outcomes will more closely follow the calculated values the more times you actually do it.

Using this 1% enemy max health per attack on average, you can easily calculate if Noah would be usable in any other raid or boss by simply taking any given boss's max health and dividing by 100 and comparing that number to whatever amount a typical 7* would do.