The discussion has stirred up a memory...
The more control you have, the more scope there is for optimization. That is, although the 4d6-drop-lowest on average produces better results than point buy, the fact that you can't determine the exact scores undercuts that at least somewhat.
Back when we were coming to the end of our 3e play, we therefore offered each player a choice:
- 4d6-drop-lowest, with a reroll for "hopeless" characters,
- A standard array of 16, 15, 13, 12, 10, 8,
- 28-point buy.
Per the 3e point buy scheme, the average for that rolled method was, in theory (and IIRC), around 30.5 points, while the array was 29.
In 5e terms, what that mostly means is that the "rolled" method is actually, on average, a good bit "better" than point buy - but at the cost of loss of control. (This method also has the scope for throwing out a 16+ score...) Note that 5e as written doesn't have the reroll for "hopeless" characters, though I'd expect most DMs apply one.
And 5e's standard array is actually slightly
worse than point buy - although the points can generate exactly that array, for almost all characters there is a more optimised option out there.
That being the case, I'd be tempted to suggest offering a choice as above: 4d6 with a "safety net", or a slightly enhanced fixed array (possibly including a 16 - indeed, possibly the same one given above), or the normal point buy as given.
At this point, though, I'm mostly just churning a bunch of ideas.
