People can deny it but it is very likely that TLoU2 underperformed.
It didn't underperform, it's a massive success in any metric and in all of them did a better job than GoT. According to Sony and ND representatives (Ryan and Druckmann) TLOU2 outperformed their expectations.
TLOU2:
-Sold over 4 million copies worldwide during the launch weekend worldwide (Tsushima reached 5M units sold worlwide in November)
-In half a year became the 3rd best selling Sony game ever in dollar sales in the US (above Tsushima)
-It's the 6th best selling game released during 2020 in the US (even if it's exclusive, and above Tsushima)
-Got a 93 on Metacritic and Open Critic (95% of critics recommend, better than Tsushima)
-It's the 3rd game that won more GOTY awards in gaming history (top game of the year, better than Tsushima)
Ghost of Tsushima is doing a great job but TLOU2 performed way better worldwide looking at sales, reviews or GOTY awards. And this is before any possible PS5 version or patch, possible extra sales generated by all these GOTY awards, possible extra sales coming PS5 once it solves its supply constrains, possible extra sales generated by any potential future DLC released with maybe the multiplayer, extra sales or revenue generated from discounts/bundles/included in services, etc.
Since Tsushima was released, it's selling better than TLOU2 every month in USA (GoT got Legends and PS5 patch), but EU is a bigger market than USA for Sony and TLOU2 performed better than GoT there these recent months. Until now TLOU2 is outselling GoT in USA (specially thanks to insane launch week sales), EU and worldwide.
To be fair AC still at premium MSRP price at Japan and the majority of Asia Pacific while TLoU 2 already at bargain bin ($70 vs $40), even GoT still $60.
I bought last month GoT (physical) at 37.99€ in Spain (top 4 European country in game sales, top 9 worldwide market). I assume it should be easy to find similar pricing in the rest of EU and USA.