I spent some time time using Blocs3 and also RW/Stacks with Foundry, and I was very impressed with how slick the whole Blocs experience was. What I found was that trying to use 2 became difficult switching between the 2 and frustrating because each one had strengths and I would often feel that I wish RW could do what Blocs could do and vice versa.
What changed for me was when Source was released in Aug 2019 and I was finally able to do everything I wanted to do with RW/Stacks/Source, and stopped using Blocs and others. I now pretty much do everything with just Source and a handful of stacks.
I do keep an eye on Blocs (now Blocs4) and it has grown in focussed leaps and bounds while RW has just stagnated with nothing new happening for years. As frustrating as that is however, for me, RW7 is nothing but a front end to Stacks and by using the right stacks it works well enough. All the current development for RW is coming from just a few smart Stacks developers. In a way this negates the single developer dependency of RW because there is no ongoing development that we can see other than keeping up with new versions of macOS. RW’s dependency is Stacks, so as long as Isaiah, Stuart and Norm don’t get on the same flight, we should be OK.
The new feature that Blocs4 can create a Wordpress template may draw me back into blocs when I next need a WP solution, but at that point I would evaluate Blocks against Elementor or whatever WP system I need to gain access to. Also the video based Blocs Academy is amazing and shows what can be done when you work hard at something.
If you are a seasoned RW Stacks user having invested $100’s in expensive frameworks and stacks and then invested the time to learn how to use RW, then Blocs or using any other Web App will mean throwing away all the RW stuff and relearning everything.
If you are new to building web sites then RW would be a very hard sell over Blocs4 especially with the quality of help in Blocs. Blocs has everything needed to build a modern website without any further purchases.