Interesting.
I may be off about a year, but, the overall best turkey hunting I've had was about 1997-2004.
While there have been some annual ups & downs, it's been more down than up since the 4-bird limit went into effect. I admit, most of my experiences have been limited to a single TN County (Stewart), but these experiences seem to be fairly congruent with other long-time turkey hunters from other TN counties that had well-established turkey flocks during the 1990's.
It kinda seems most of those counties with the most turkeys in the 90's have (relatively) gone downhill most, and it's been much the "newer" turkey counties that have camouflaged this downturn. Not to mentioned, a lot of "newer" turkey hunters who never experienced the routine daily gobbling of 6-plus longbeards, which seemed to be more common statewide during the last few years of that 2-bird limit, and it was more this extra gobbling that made the hunting exciting than how many birds we could kill.
Never mind that I've spent much time and money improving habitat in my turkey hunting areas over the past 15 years, and by most measures, the habitat is now significantly better for turkeys than during the late 90's.
How much did the higher limits have to do with this decline? I don't know. But I'm positive they have been a factor in that decline, and reducing this 4-bird limit is at least one step that could be taken to help. And at this point, I believe there is much more reason to lower that limit than there ever was to raise it.