Hi Sean,
I can certainly empathise with your experience - Magento is definitely more complicated to set-up and customise initially. And for a little background, I worked on the early versions of WooCommerce with the original developers, so I understand why there has been a need for simpler, more effective eCommerce solutions.
With Magento, the key is to find developers and agencies/consultants who have experience with it. Like any platform, it's much easier when you know it well, but often we don't have time to spend learning before we're earning. I've worked on 2-3 fairly big Magento sites now, and can get stuff done reasonably quickly and cost-effectively, but it's never quite as fast as with Shopify or WooCommerce (although knowing some Magento specialists makes a big difference).
This article about a large company moving to Shopify sums it up - from the article it's clear they had appalling developers, but used that as the reason to switch platforms (http://elumynt.com/magento-to-shopify-plus-complete-guide-for-large-retailers/). I can't blame them for it when it was costing them money and business, but it's pretty clear it's a dev issue...
And Shopify isn't bad for what it is. If you're looking for something that is more plug-and-play, it'll do the job.
The problem is always that you're limited by what's available. So if what you need hasn't been created/verified/approved, you're basically stuck. From memory, a team I know have put together some SEO solutions for Shopify so will try and dig it out.
With regards to any migration - if it's done properly, you shouldn't lose rankings. I've moved tens of thousands of pages across domains and CMS platforms etc, and had minimal drops if any. Usually the new platform etc has been rolled out to improve things, so it often leads to a gain even if everything else stays the same, just because the new set-up is faster etc. The key is to plan out the switch very carefully and with plenty of time to check, double check and triple check - 301 redirects, .htaccess and robots.txt files are the essentials