Any top player in the 2018-20 period would have beaten Siegemund comfortably. Maybe not 6-1, 6-2. But look at the 2019 Wimbledon semis, and how easily Serena and Halep won. Their opponents were way better than Siegemund.
Also more damning is that Sabalenka never went far in the slams in 2018, 2019, or 2020. She was aged 20-22. She only started to go far in slams in the 2nd half of 2021, at age 23. Of course, this coincided with players like Serena, Osaka, Barty, Halep, Andreescu either dropping off or retiring. If Saba/this era is so great, why didn't she win during that strong 2018-20 era? And you can't use age because Saba in 2018-20 is older than current Mirra Andreeva.