No. More games won't result in decrease in quality of games. That's bullshit.
Actually playing the game is the best practice and see which things work or don't work against the team you prepared for. Rematches in such cases are really good quality of games.
Also, just VOD reviewing is not going to improve your game, even it did, more games would equal more VODs. NBA is the extreme end of having number of games, 24 games a week in Valorant is nothing.
Riot is just stupid and thinks that it would mean overlapping EU and NA games or some other region but that group of people who watch multiple regions is less anyway. More games per week would actually increase the total views. Just because Sen is playing twice, doesn't mean who are not going to watch them 50% of the time. In fact, you will watch 1 match and maybe half of the other (overall increase).
Also Riot doesn't need to keep two matched at the same time. They have Monday to Thursday for it. They don't do it because of League bullshit.
Most of the prep for teams is not about just "antiying" the opponent it is to drill their own protocols and strats which they can do regardless of how many matches.