If the closed beta can't handle the load, then that's gonna look bad for Microsoft lol. Since part of the reason they wanted to help bring PSO2 over, is to "show off" their Azure cloud servers. Which supposedly they are using their best kind of servers for PSO2 NA. (by sounds of it*)
At least I'd like to hope that should mean it's unlikely to have that much server performance issues, but guess will see.
*This is from some "behind the scenes" interview that had someone from Microsoft and Sega, about their development/collaboration on PSO2 NA/Azure servers. (https://www.gamebusiness.jp/article/2019/07/22/15987.html, It's in Japanese but Google translate doesn't seem that bad >.>)