SAFe seems to sort of be a micro-waterfall approach inspired by Conway's law [1]. It build massive communication and coordination teams so that this gets reflected into short-term development waterfalls that produce software that mirrors the system that managed it. But this team needs to be dwarfed by the development effort they are trying to push forward or they'll end up dominating all of the activities with largely useless communication and coordination activities resulting in very slow forward software movement, confused goals and priorities, and overstaffing of projects.
Example: I once ran a team that was developing some internal tools for a large org, but we were outside of the main SAFe effort. At one point we became dependent on some service the SAFe effort was going to produce. It took 60 people 3 years to not produce a correctly working service. Exhausted with this, I finally just had 1 person build the service we needed as a stopgap. She spent 3 months building it with part-time support from one other engineer for a couple weeks. More than 3 years later that is the service that's still running and the SAFe effort never did manage to get a properly working solution out the door. I can think of half a dozen similar examples where the parallel effort by a smaller team with less organizational overhead radically outperformed the giant SAFe team -- and they did it mostly by just ad hoc communication channels between the small teams.