Haven't I debunked you on this exact line before?
That line is entirely smoke and mirrors. Frankly you'd have to be an utter imbecile to think that they somehow need to use addons to test content in production. They can simply use development clients to use things such as godmode, inflated damage and hp, even break fights down into a phase by phase test if needed. This was something that was clarified very specifically by Yoshida back in Gordias and other than them switching away from testing phases individually (with fresh cooldowns which was a big part of the Gordias tuning issues), nothing appears to have changed.
If you seriously think that SE's testing team was clearing DSR entirely legitimately during it's development then I don't know what to say to you tbh.