Never open servers for people earlier then it goes live. It has negative impact on perception and also causes people to have a unfair advantage. Not a big thing for CoF but for MG players it definitely causes problems inherently.
Also it’s not said that the testing environment is even playable, usually development is not a straight-forward linear process. A mechanic implemented in a specific way can be adjusted days before release even if something easier and better understandable is found. Wouldn’t be the first time it happens. So would your results still even function as they need to be removed maybe? Or have you gotten a massive upside/downside comparatively to what others will experience?
Also… would you keep the characters of the testing environment? If so it’s not a fair cycle start… and otherwise you would need to re-do it which people often are averse of.
It’s not a good thing to do in general, too many places which become ‘rigid’ when opened up for players.
Instead of beta, it could be labeled a pre-release server stress test or something (insert your own scenario). Character progress in legacy could carry over, but the season 2 start would be 2 weeks later.
Have you also asked GGG if they can postpone it?
Honestly, LE shouldn’t be postponed just because some people are bothered by it. They just need to pull themselves together and decide what they want to play.