It looks identical with or without the soft hyphens. Decent renderers do hyphenation fine without them and some don't use them. In fact I've never seen soft hyphens directly inserted like that in any ebook I've edited.
I have no control over what apps and ereaders other people use or how Amazon converts an uploaded epub (on KDP, we don't used Send to Kindle) to mobi, azw3 and kfx and chooses which to deliver to the customer.
A more serious issue is the need to hand edit the epub. Not practical for 20 to 40 revisions of a 150K word wordprocessor source to docx automatically converted to epub by Calibre. I will look at how MS Word and LO Writer can do two columns in a manner that works automatically with conversion.
There is no such thing as a single Kindle solution for KDP (or even direct sideloading), unless there are a load of Amazon specific media queries, which break the workflow and don't always work as expected. There are old ones that only do kf7/old mobi. The ones that do azw3 don't all behave the same. Some do azw3 but not KFX. A Fire isn't a Kindle, but runs a slightly different Amazon Kindle App built in to the Kindle App on Android. The Kindle App on iOS behaves differently, though it may soon be better. There are Kindle Apps for Mac and PC . All of these behave a little differently. Also there is no way to insure a user selects Publisher option.