If you want to store movies and music on your iPad, then that extra $$$ for storage shouldn't count as a necessary cost of using your iPad for work.
How much storage do you need just for apps plus work documents?
That said, maybe something like the SP4 is more suitable for your needs, and that is perfectly fine. Not everyone has the same needs and preferences. My Mom fell in love with the iPad Pro at first sight, but I couldn't get her to even glance at a SP4, lol.
Trust me, I want to make it work with the iPP. The SP4 is not a bad device but based on all the recent reviews, it's buggy, and the battery life isn't nearly as good.