I don't think it should require "17+ total points" to bid 4 diamonds. And 4d should promise at least 5 diamonds not 4. (forcing).
I think East's lower bound should be a tad higher, maybe 13 or 14 total points, and West should be allowed to bid 4♦ on maybe 11 or 12. It caters to getting to the right strain for game, vs. getting to slams, although sometimes 5m may be a bit too high, oh well.
Requiring 17+ for West is just too much, you miss too many games. East needs to give West some leeway to get to diamonds without bidding 6.

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