So, it goes without saying that in order to get more flexible, you need to stretch. Dynamic stretching before workout, static stretching after.
But does the act of kicking itself help one get closer to a full split? In other words, if I stretch every time I work out for a year without doing any kicking at all, will I become flexible more slowly then if I were to spend all of those workouts doing nothing but practicing kicks (as well as stretching)?
Yes, kicking helps flexibility. I suppose you could say it's affect is indirect.
If you look at purely flexibility, elasticity of muscles, joints, mind, etc... you could picture your leg as a rubber band. 1,) Pretty useless setting on a table. 2,) Pull it back, and you have a tension spring that will create force but will have very little control. 3.) Aim it, using you own faculties, (eyes, hands, etc...) or a tool/toy to aim and shoot the rubber band, then it becomes an effective 'weapon'.
If we apply this logic to kicking, just stretching results in the rubber band setting on the table (1).
Stretching and
unfocused kicking would result in idea 2.) where a person may have high but weak and inaccurate kicks and lack the inability to chain kicks or incorporate other movements.
Incorporating both stretching and kicking with a focus is what you want. But understand!!! Uber high, flashy, and even fast kicks take MUCH longer for some folks. Just the differences in body types, time available, etc...
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To the second part of the OP, no, I guess I would have to say kicking would not speed up getting a greater stretch. But the question becomes what would you do with the added flexibility if it not usable?
You are right on track with you dynamic/static comment. Assuming you do partnered pad work, drill the higher kicks. Not all the time but often. Then apply them with resistance (drills or sparring).
Remember, this is a marathon, not a sprint. In the bigger picture, and year can be a short amount of time.