I agree with the fight not being as sakuga as say a big fight in Demon Slayer for example, but it depends on how you look at it.
For TV-only animation, the fight was decent quality.
The Solo Leveling theatrical release did not do particularly well in Japan, and famously the DVD/BluRay release bombed.
Not surprising, especially given how negatively the Japanese Hunters are portrayed.
SL just isn't as popular in Japan for that reason, so TV revenues there are limited at best.
Anime adapted from Korean manhwa sources tend to be unpopular in Japan anyway. If you look at Tower Of God S2, a manhwa adaptation on the graph in the article.
So their animation budget was always going to be limited to the revenues from the international market.