The answer is simple: Straight rotation, as played in the Phillipines.
1. The game has a Power break, which translates well to many other games.
2. The game has kicks, banks, combos, caroms and any other shot that comes up in other games. More importantly, you are rewarded for shooting these shots! You can argue that all of these shots are present in 9/10 ball, but the fact of the matter is, since you have to run out at these games to win, that it often doesn't pay to shoot them. A 10 ball match between non-pros, often turn into a total safety snoozefest.
3. In other games, safeties are given so much value because of the ball in hand anywhere rules. Not so in rotation. You need to be able to kick well and shoot big shots to win at this game. You can't just roll in two easy balls and play safe, then expect to win easily. It's not how the game works.
4. The game has 15 balls on the table and you have to run them in rotation. This means playing around and into clusters, with control. Filipinos play every game well, because of this.
5. The only thing not taught by rotation is pattern play (in the meaning of shot selection). You can't choose which ball to shoot so you lose out on a bit of 8ball and straight pool strategy. Usually the good players are quick to pick up on that skill, anyway, but that is an acutal lack in skills taught by rotation played exclusively.
6. The fact that the game does not have called shots, is a strength! It teaches the player to play two- or even Three-way shots, to be creative. This is a skill that may be lacking in players who play exclusively with call-shot type games.
One Pocket is not a candidate. Many of the standard shots in one-Pocket are highly specialized and do not translate well to other games. Much of the knowledge is negative, meaning knowing which shots to avoid. At the highest Level, you can't be ducking shots in any other game. You have to shoot to win. One Pocket is a game for the mature player, who has knowledge from other games. It's not a teacher of shots, other than the specialized ones.