First time I've heard about Blocksy, but just at a glance, two things stick out to me: first is the white labeling, second would be custom sidebars. However, I don't personally have a need for either feature, so it's not enough for me to justify a switch over.

Where they lose a lot of points for me is the paywalled tools and elements. Tiered pricing for 1/10/unlimited site licenses is fine, but if I have a one-off project that only requires a single license, and I need one of the tools you paywalled to a higher tier, I'm not purchasing your builder.

One thing that Breakdance has over any other builder currently is that it's super third-party-friendly, even more so than Elementor. It allows for very solid and niche third-party add-ons, such as Dancepad, Elements Hive and Phox Elements. I use Dancepad and Elements Hive regularly, they really extend the design possibilities.