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I don't think it is a smart move to use 10% of your capital as withdrawal fee, that is too high for me. Instead of doing that, you could buy weekly but withdraw monthly, this way you will be cutting down the fee to 2.5% of your capital. If you continue to spend $5 as withdrawal fee for a $50 weekly DCA, that will amount to $260 annually as fee which is too high for such a low capital. So lile I said before, instead of this, a weeklg DCA and monthly withdrawal will be better.
What I'm suggesting to you is also what I'm doing because we have to maximise the opportunities while cutting down the cost of doing that.
I think your suggestion would be good for those on a low budget, say $50 per week. They can withdraw their bitcoins to their wallet within a month or after they accumulate more bitcoins to save on withdrawal fees instead of withdrawing every week. Of course they can choose a trusted and reputable centralized market to avoid many unwanted risks, but they can also choose which step they want most.
There is no pressure to withdraw every purchase or withdraw after a few purchases, it really depends on how they do it. The bottom line is, bitcoin should not be held on an exchange for the long term because of the risks.