As you know I was working previously with Foundation in RW and it was capable in terms of features, albeit with help from third party stacks, but yes the lack of speed was just horrendous and became the primary reason I ditched RW for Blocs. In RW it would take 30 seconds to preview a page with an image or two and some text at desktop, then another 30 seconds at tablet etc. The same pages in Blocs would flick between breakpoints instantly.
Unlike Blocs you need to preview much more often in RW as well, so this becomes particularly painful. If I open up RW now the interface with a lot of those stacks is a complete mess of complication with functions that can often be achieved far more quickly at no cost in Blocs.
I think a key difference is that using Blocs actually teaches you a bit about web design, where I only felt like RW was teaching me how to use RW. The learning curve in Blocs is perhaps higher if you want to do more than the basics but overall I just find it a far more pleasant and productive place to spend my day.
The new version of Foundation is said to be faster and it’s probably very good but it took about five years to appear and I haven’t tried it. I find it a pain going back & forth between apps that work in such different ways, so I am sticking with Blocs.