If you use that speaker, sure it's subpar. But a lot of us don't.
The only times my speaker ever makes noise is when a timer/alarm goes off, I get an unexpected phone call and need to hold the phone to my ear, or I am on a FaceTime with family and my 4-year old is around and wants to talk too. Otherwise I am using AirPods.
I suspect that those use cases won't be harmed by one speaker. If you listen to music on your phone, or watch movies/shows/YouTube without headphones, then absolutely it leads to a subpar experience. But for me, personally, lack of the second speaker plays zero part in the decision; in fact, I suspect I'd rather have the extra battery than the space the speaker takes up.