Do see your point, center channel also being the dominant channel in surround. Still though adding a two channel amp or two monoblock amps will take the load off of the power supply, Allowing the AVR amp to supply All it's power to center and surrounds.
My Yamaha 7790 has full pre amp outs I had Multi channel amp 200 X 5 sold it off cause I found that at Moderate listening levels I couldn't tell No difference. For my use I sit right at 8 ft from my 4K tv and center channel sits right under my TV. So In reality that 5 channel 200 X 5 was overkill didn't need it. Now for those who have larger rooms and sit back 10 ft or more may need a added amp or if there driving less Sensitive speakers. Yamaha has their a780 I believe has L/R mains pre amp outs so does their older 7850 their older 7810 has pre amp outs for all channels. But yeah I Definitely get it about adding a amp. With this hobby some even I just like Multi channel amps in our setups.
So this has always been an issue I've battled back and forth with. Of course I want a nice set up but I always try to curb the desire to just be stupid and get something ridiculous and over the top, so I'm basically always trying to compromise with myself.
I live in a townhouse with an open living room/kitchen level, sitting position is about 10ft from speakers but it's in a large open room. My speakers take 20-200 watts, but I figure my 50wpc Marantz 1609 is providing maybe 35wpc driving 5 channels. Well within the minimum range, but far from optimal.
It sounds just fine, but I always hate that I have to crank the volume on the Marantz; my default power on volume is 55, out of 98. I usually use it between 45-65, but sometimes over 70 depending on the source (Apple TV is super low level for some reason).
It just always seems like I'm wringing it out, a 3x 200w external amp seems like a perfect solution, but my AVR only supports L/R pre-outs. If I were to ever get a new AVR now I would never consider buying one that was not future-proofed for the PS5/etc. so HDMI 2.1 is a must.
But the idea of paying double for a receiver just to have multi-channel pre-outs and only one 8K input just doesn't sit well with me, I would much rather get the external amp and just use it for L/R while waiting for new 8K models come in the next few years.