ODI cricket would be way better if the power plays were chosen by the batting captain?

I agree with you on that on point. It would make more sense if it was the batting sides choice because the very term "power play" insinuates that there is some advantage to be had by playing the "power play". There is no advantage to the bowling side during this period, so , as you say, the batting side should have the option of choosing when to play the "advantage". Whether this is after the batsmen have got their eye in, or after the best bowlers have been seen off by the openers, or near the end of the innings when the run chase is a close game. The way it is played at the moment, they may as well just say" the 1st 15 overs of each innings have fielding restrictions" good Q.

Yes,I agree the powerplay is only six overs as in twenty-20 game.

I agree, this would be really good in the last 5 overs.