Minimalist (?) turn undead, plus a reflection on playtesting

Here is my minimalist version of turn undead, which precludes the need for a turn undead table, and uses 1d6 instead of 2d6 plus another 2d6 plus table:

Turn Undead: Clerics can repel or destroy undead. Turning is attempted once per turn, in lieu of an attack. Turned undead flee by any means available and will not harm or contact the cleric. To turn undead, roll 1d6, add the cleric's level, and subtract the target's HD (e.g., 2 for zombies). A result of 5+ succeeds; 10+ simply destroys them permanently. The roll result also indicates the total HD of undead affected (minimum one creature, maximum 20 HD affected). For example, if you roll 11 against zombies, 5 of them are destroyed; against skeletons, 11 are destroyed.

This is the type of rule I want for my game; maps reasonably close to the original B/X (at least to my liking), but a bit simpler, faster, leaner, easier (it also expands to RC levels).

(I can take no credit for it as apparently Delta wrote something similar more than a decade ago; since I take much inspiration from his blog, I might have read it at some point).

In practice, however, I found that this is not enough for even the simplest games. If using this rule (or even the original B/X rules), the players will certainly ask simple questions like "how often can I turn?", "how far", "for how long", etc. It happened in my last campaign.

And the text simply doesn't say. The Rules Cyclopedia adds a much longer text (and table) - but not many answers either. Same in the AD&D PHB.

5e D&D, on the other hand, clearly answers all these questions (30-foot radius, 1 minute or until the creature takes damage, etc).

I'm probably adding such details to my own game since they were obviously needed at my table. So my version might even look a bit longer than B/X, which wasn't my original goal. 

Old school D&D seems to work very well in practice; people often say it is because Gygax etc. had immense wargaming playtesting experience. But I have a feeling that old school GMs often relied on their experience and rulings over having things spelled out in the book, which some people may appreciate but certainly brings endless problems when you don't have much experience with a system and need to learn from the book.

In other words, these games were likely playtested by people who were familiar with wargames, instead of given to newbies to see how understandable they were.

Modern D&D is much more complex (and even verbose and repetitive at times) but often better explained. And, to be honest, I don't think you can get "minimalist points" by omission and incompletion. If the book needs a "good GM" to work, it is not a great book, as most GMs are average by definition (or, at the very least, the book cannot take much credit for the rules if the GM has to create most of them).

Anyway, I keep looking for my ideal D&D - say, something as simple as B/X but as clear as modern D&D. This, I hope, is one step in that direction.