I'd say that practice produces quality, not necessarily quantity. Something I only learnt at the start of this year (2018) was that even my best pieces of writing needed oneheckuva lot of editing instead of just sending off the first draft. That's why I was so quickly rejected... I had wrongly thought that my first, totally unedited or even looked at since writing it, draft was perfect.
Those first rejections really hurt, but I can totally see why they were rejected now and totally agree with the rejections I went through now. Editing should be your friend instead of your enemy! Finish that first draft, write the synopsis then forget about it totally for at least 3 months before you edit it for the first time. You're not allowed to even glimpse at it for those 3 months, you've got to totally forget everything you wrote, then that first day of editing will throw up all kinds of hidden errors that you had unintentionally overlooked while you were writing it. It might be a misplaced full stop (period for my American readers) or comma but it could be a huge gap in the middle that you know happened in your head but it never made it onto the screen. Things like that get you (and me) rejected but is easily fixed with a bit of editing.
According to the book I borrowed from the library, Ray Bradbury advised authors to "write a short story every week. It's not possible to write 52 bad short stories in a row" and I kinda agree. Steve (the hubby and in-house-geek) chuckled and said "I'd give it a go!" and while he said it as a joke, he's just summed it up perfectly... write something every week and with practise you'll come out at the end of the year with 52 stories that can be whipped into shape either almost straight away (if you're a PB writer) or edited to wonderfulness and hopefully being accepted by the publisher or agent of your dreams!
Apparently Richard Branson (of the Virgin Group of businesses) was (and possibly still is) a real blagger. I'm starting to become like that... what about you?