I think the point is that for
dialog, frequency response is not as critical. If you are watching a concert, sure I can see that freq response would be more important but almost everything else clear dialog is more important. I have a decent Polk center channel that actually sounds pretty good but before I had it, I had a cheapie and it did the job pretty good for normal volume TV watching etc.
Here is a pic of what our living room setup looks like. We have a small front room and I love both two channel vintage stuff AND modern HT sound. So I have a Marantz 2220B with Marantz TT driving two Marantz Imperial 6s. On the left is an older Marantz SR 4002 AVR and under that is a Marantz DVD/SACD that outputs HDMI to the AVR for DVDs and analog outs to the 2220 for CDs. I have a Playstation 4 under those for BluRay playback. The Imperials are at seated ear level in front of the couch. The front mains are mounted low in the TV stand and are Realistic Minimus 1s. They are really mounted too low to be optimal but since they dont do much work and the Polk center is tilted up, it sounds amazingly good. The back surrounds are Minimus 7Ws and next to the couch under my computer desk is a Sony sub. The Marantz AVR has 80 watt discrete amps and MRAC room correction and sounds really pretty good.......way better than it has a right too with such a funky front setup. Since we live in a condo and really cant get the massive sound levels that some run their AVRs, it works just fine for us. In the morning (we get up at 0430 for the wife to be at work at 0600) we just use the TV speakers since we need to keep it quiet. When watching TV shows worth it, we turn on the AVR and enjoy the surround sound......I also use it when using the Playstation and it is amazing.
We watched an old DVD the other day of Michael Buble' and was surprised at how good the Polk center channel was producing music and his voice. So I guess I mean to say there is not
one solution for every show or movie. But modern TV/DVD/BluRay simply sounds better with at least 3.1........on the type of shows that have high production values. And if you have the room, rear surround speakers make movies really fun. I had the 7.1 setup for a while and it did not make enough of a difference to overcome how it looked in our living room so I went back to the 5.1 and am completely happy.