I dont think that it hurts viewership, maybe on the main broadcast, my example ( and I know i'm talking extremes):
There is a Furia x 2G game, followed by Sentinels x G2.
First match you get like 30k~ and on the next one 100k~
The following day you get Cloud9 x NRG with 60k followed by Loud x MIBR with 70k.
That would average 65k~ viewers through 2 days, 4 match slots
If they were to happen at the same time, for day 1-first slot you get Sentinels x G2 on stream A with 90k viewers, and Furia x 2g on stream B with 10k viewers. For day 1- slot 2 you get Loud x MIBR on stream A with 50k viewers and Cloud9 x NRG on stream B with 40k viewers.
But since 2 games are happening at once, you get games on other days that you wouldn't get otherwise, like G2 x Furia, 2G x Sentinels, Loud x Cloud9 and NRG x MIBR, and even if some of them are blowouts, or don't attract that much audience, you get some games that are worth watching anyway.