When did 32" panels weave in? If Apple wanted to get a 'larger iMac' onto the market because it was 'needed now' it could have come in the same form factor they already had. Just like the Mini, MBP , MBA. More likely Apple is waiting to more past the IPS panel era. ( whether that is OLED, mini-LED , micro-LED , etc. )
It is pretty unlikely that Apple will pick up that 6K panel tech when the price has dropped so far in just a couple of years. One of the factors that propped up the 27" iMac for a long time was that the PC market 'quit' on the 5K pane; not that they were using it in volume.
that 5k and 6k have 'general PC monitor market' models which are getting more affordable each year is iMac 'liability' not an asset for competing with non all-in-one solutions.
6K + Mini cheaper than iMac ... hence the 'problem' for the 'large screen' iMac. 5K monitor would probably even a bigger cap. A 4K monitor an even bigger gap. Once the Mini is somewhat artifically throttled then have issues. ( there are reasons why all-in-ones don't dominate the general PC desktop landscape. ) Apple unilaterally designated iMac king of the desktops in the Intel era and took steps to make that skew that way. IT wasn't primarily driven by market demand from the outside.
This is really shallow examination of specs that. consists only on price (which really isn't even a technical specification. More a marketing specification. )
Leaving out the Mini Pro options isn't about cadence. The iMac 27" with only a plain Mn , when there is a Mini Pro available is problematical in terms of fratricide. Folks who need additional graphical performance are just going to pass up the 27" model limited in that way.
Not really. Apple could change directions, but the 27" model was more GPU focused ( as are the Mn Pro, Max . etc) . Below is a sampling of 21.5" iMacs followed by 27" of same time frames. [ first set goes backwards in time and then 27" goes forward. ]
the 'base model' 21.5" had an i5 toward the end.
2017 Core i5 (two cores) iGPU only ( Iris Plus 640)
support.apple.com
2015 Core i5 (two cores ) iGPU only ( Intel 6000 or 6200 )
https://support.apple.com/en-us/112036
2012. Core i5 ... pseudo dGPU ( pragmatically iGPU Nvidia 640M 512MB VRAM whichhas no display out. Discrete but not a complete end user GPU either).
support.apple.com
The gap between. 21.5" and base 27" was on GPU , not CPU.
Yes in more ancient days there was a core i3 in the iMac 21.5" ( and anemic dGPUs )
2010 Core i3 dGPU ( ATI Radeon HD 4670 graphics processor with 256MB of GDDR3 memory )
support.apple.com
2011 Core i3 dGPU ( AMD Radeon HD 6750M graphics processor with 256MB of GDDR5 memory )
A whopping whole 256MB of VRAM ... whoo whoo .
But there were also. i3's in 27" models too at one point. But the GPU's are substantively better than the 21.5" model
2010 Core i3 dGPU ( ATI Radeon HD 5670 graphics processor with 512MB of GDDR3 memory. option for 1GB VRAM ) [ vs 256MB for 21.3" ]
support.apple.com
2011 Core i5 dGPU ( AMD Radeon HD 6770M graphics processor with 512MB of GDDR5 memory. options up to 2GB VRAM) [ vs. 256MB for 21.3" ]
support.apple.com
2012 Core i5 dGPU ( NVIDIA GeForce GTX 660M graphics processor with 512MB of GDDR5 memory . options to 2GB VRAM) [ vs Nvidia 640M and fixed cap of 512MB ]
support.apple.com
2015. Core i5 dGPU ( AMD Radeon R9 M290 graphics processor with 2GB of GDDR5 memory) [ vs Intel iGPU ]
https://support.apple.com/en-us/112434
2017. Core i5. dGPU ( AMD Radeon Pro 570 with 4GB of VRAM. option for 8GB VRAM) [ vs Intel iGPU ]
support.apple.com
[ Aside the 2020 27" iMac topped out at 16GB VRAM with an AMD Radeon Pro 5700 XT. That is better than the Mac Pro starting point in that era. ]
The long term consistency is the that GPU is always better in the 27" than the 21.5" ; pointing at the CPU is a bit of misdirection. [ The GPU was a 'herd them' factor of folks into the 27" model. ] And the i3 was in the 27" at one point and the 21.5" had i5's toward the back half of the Intel era also. The 27" model also better memory options for end users. (e.g., max memory at more reasonable pricing).
The Mini pragmatically needed a Mn Pro model just to get close to what the Intel Mini 2018's max memory capacity. If need generous amount of RAM then the plain Mn isn't a good option.
Apple isn't really doing this, but it is closer than what you are proposing:
Mn - i3. , Mn Pro - i5 , Mn Max - i7 , Mn Ultra. - i9.
If the line has 4 levels, there is no way the plain Mn model is in the mid-range. However, the plain M5 (and follow ons) is probably fast enough for most people in general population.
The big gap there is far more on GPU cores , not CPU cores. (apple's agenda is to get rid of Intel/AMD GPUs as much intel CPU cores ) However, GPU is one of the major differentiators for Intel era iMacs.