That said, they do seem to be going through--or have recently gone through--a fair amount of attrition due to declining stock prices. Not surprising given the stock situation and all, but definitely something to factor in if you're considering working there.
EDIT: I'd also like to mention that it was a very humane interview process. I felt well treated, and they definitely seem to be screening more for successful employees than they are to filter out as many applicants as they can. Take that as you will, but I respect an org that treats it's employees well.
Just because you had a bad experience doesn't mean all of Shopify HR is very slow.
This goes for all tech companies not just Shopify. Many people believe that because the recruiter they were dealing with was slow, that must be the case for every candidate across the entire company they are dealing with.
As with all things in life, remember YMMV. Hiring is crazy right now at all tech companies.
Interviews often set perception of how well a company operates. If you or your company care about your reputation, get it right.
Google/Alphabet is still suffering from it's reputation for horrendous interview experience well after a year or so of getting things back on track. Reputational issues are sticky, be they deserved or not.