When we build furniture with loose tenons, the size of the tenon alone does not determine everything. How well the fit the joint itself is, how other components (e.g. braces, stretchers, back panels, etc.) are used, and how the glue-up is done also affect the structural strength. Before the DF700 was released, everyone (owners of DF500, that's) was using the DF500 to build things with great results.
I'd definitely buy a DF700 if I am to go for building big entrance doors, huge workbenches and the like. But none of them are on my "to-do" list in the foreseeable future. I'm only a furniture maker.