NCT sold around 10.9 million albums this year (including Universe reported sales which aren't out yet in the Gaon december update)
and this is the list of the reported 2021 sales for the biggest companies
so with their above 10.9 million albums sold, NCT not only represents more than half of the total SM's 2021 sales (17M), meaning that excluding them, NCT is selling more then SM as whole, but they also OUTSOLD other companies... even taking into account the japanese releases from Oricon chart when it comes to JYP, YG and Pledis
NCT can be their own company at this point and they could rank in top 3 for album sales easily...