The Scrum Guide defines a single unit that consists of a Product Owner, a Development Team of 3-9 members, and 1 Scrum Master for somewhere between 5 and 11 members. I've seen instances where the Product Owner may have support staff or the team may not have a dedicated Scrum Master to vary that number slightly, but it seems to cap out at about a dozen people.
The Nexus Guide describes one method of scaling Scrum to handle 3-9 Scrum teams working on a single product. It adds a new Nexus Integration Team which may be dedicated members or it may be composed of people from the various Scrum teams. Based on that guide, it would scale to about 20-120 individuals.
Disciplined Agile can scale up from one team to N teams. A standard individual team size would be about the same as in Scrum - 3-9 members plus supporting roles from various specialists, independent test teams, domain experts, etc. The considerations in this framework aren't simply scaling, but applying the agile methods in large organizations, regulated environments with mandated compliance, outsourcing, globally distributed teams. It seems like the limit is that you would have one instance of DA per product or product line.
To varying degrees, I've been involved in working on or implementing processes using Scrum, Nexus, and DAD, so I have a solid understanding of those. I don't have a working knowledge of LeSS and SAFe, beyond what I'm reading other people saying.
LeSS seems straightforward. It's an alternative to Nexus that has the capability to scale much larger. The rules of LeSS state that LeSS is designed for 2-8 team and LeSS Huge is designed for 8+ teams, which I would estimate the development organization size to be at about 15-80 for LeSS and 80+ for LeSS Huge. Depending on your organization, you would probably be looking at 20-110 people in the product organization for LeSS and 100+ people in LeSS Huge, counting management, independent QA, operations, and so on. Both forms of LeSS appear to be geared toward a single product, or perhaps a closely related set of products (such as a product line or set of microservices). Every product would have its own instance of LeSS (or LeSS Huge).
SAFe seems to be inclusive of the whole organization - operations, user experience, enterprise architects and systems engineers, product managers, QA, developers, and so on. It has two models - a 3 level organization and a 4 level organization. The 3 level organization identifies Team, Program, and Portfolio. The 4 level organization adds a Value Stream level between Program and Portfolio. Based on the number of roles identified, it seems like this is targeting large enterprise organizations with multiple products and concurrent programs. Reading their guidance for implementing, it seems like they expect an implementing organization to train executives and management and then at least 50 members of a development team. Minimum organization size would seem to be a couple of hundred people across all of the identified groups and multiple products to make implementation make sense.
Am I right in my assumption that LeSS is a "competitor" to Nexus with respect to the target audience and SAFe is targeting very large organizations with a large number of products or product lines, far more than the other scaled agile frameworks are?