Ever measured the response of your current center channel? There could be a null in a critical range that makes dialogue difficult to understand without the center channel being cranked up. It could be that your center channel's crossover was designed to have the tweeter wired out of phase, but the assembler wired the tweet incorrectly causing a severe dip around the crossover point. Or maybe there's a lobing problem if you sit off-axis. Or maybe there's a placement issue causing a suckout. I see
in your front stage photo that your center channel rests against the front wall. It's not rear ported is it? Anyway, measuring the response might help you solve this mystery.
I used to turn my previous center speaker up about 6 or 7dB louder than my mains for intelligibility. It also sounded boxy at times -- not often, but enough that I eventually upgraded. My current center is now about the same volume as my mains, because it's a better center and easier to understand dialog at lower levels.
But upgrading the center channel was not simply a matter of swapping out drivers in an existing cabinet. To answer your question:
No. This is not a good idea at all.
As I mentioned in post #12, there's a lot of knowledge, time, and effort that goes into designing a worthwhile center channel speaker; and replacing drivers based purely on their sensitivity is a recipe for disaster.