Hi and welcome to the forum:
The term 'prosumer' is, of course and engineered one, combining the terms professional and consumer - that much is obvious. There is a colloquial hierarchy as regards the status of a camera:
Professional suggests a camera of extremely high quality and performance that is built for the rigors of professional use as a tool and has the longevity to last a professional for some time, including such things as build materials and weather sealing. They have dual memory cards, use large capacity batteries and have battery grips.
You might be surprised how many professionals hold onto their cameras far longer than enthusiasts for example. For many working professionals trust in the reliability of their gear is often more significant than the latest knobs and dials. For example, the pro bodies don't have things like auto scene modes available on the mode dials, but do have more options for setting up custom configurations. That is also reflected in how much longer it can be between the release of professional camera bodies. So, professional gear is not only built like a tank, but supported for the longest of any range of equipment as regards service. As far as Canon bodies would go, I would personally include the 1D, 3D, 5D, 7D (the latter as their pro APS-C camera body). The new R-series bodies generally follow that convention. The R1 will be their flagship, with the R3 is more biased for pro sports, R5 for general purpose, but IMHO the R7 is not up to the level of professional quality as regards features and build, but that's a different discussion... All of these R-series bodies use the larger LP-E6NH batteries and (except for the R7) battery grips, and have IBIS, while lower end ones do not offer either. R-series now all have flip screens.
Enthusiast cameras will have lesser weather sealing, offer scene mode options (like presets for portrait or landscape), controls that can be customized and have flip screens. They are almost always APS-C bodies from here on down. They will be, as the name suggests, aimed at serious students, enthusiasts and even part-time professionals who want good quality APS-C bodies. They are numbered as XXD DSLRs, like the 40D, 50D,... 90D being the last in line. In the R-series, I would say the R7, R8 and R10 are examples. They are refreshed about every 3 years and have a moderate support life.
Consumer is aimed at a different market. The level of many hobbyists, and those for whom the budget cannot extend to more expensive gear. The models are not as ruggedly built, have shorter service support lives, but are updated frequently - often every year or two. They often have features such as flip screens, more auto mode controls and a range of buttons for various features, Around the world (except North America where they are the Rebel line with no logical numbering that I can fathom, and in some parts of Asia where they are known as the Kiss range) there is a consistent numbering system. So consumer cameras would be ###D series: 350D, 400D... 850D was, I believe the last of the line. This has not so far been followed with the R-series bodies, but it's still early days, but it looks like the R100 may be an example of this.
I would add another level below that. In DSLR terms, these would be cameras with a ####D ID, such as 2000D or in Asia the Kiss 2000 - North America still used their unique naming system. These have the cheapest build, no flip screens, reduced controls but easy options for automatic use. They have the least support lives (to my knowledge) and are refreshed about as often as the Consumer level camera bodies. They are great for casual users, students, or those on a minimal budget.
So Prosumer sits on the cusp between Professional and Enthusiast However, there is no hard and fast definable threshold between profession and enthusiast/consumer level. In essence, these cameras may be used by some professionals as primary and/or secondary cameras, or by serious and reasonably well-heeled enthusiasts. They embrace cameras like the 6D series of cameras, but include the 7D (some amateurs will pay the extra for a top end APS-C body), but may also include the ##D bodies in some cases. So here, it is arguably the type of use and user rather than the feature set per se - they could include serious enthusiasts, part-time professionals and some professionals who will use them as back-up cameras, or if they don't need the extra build and support, by full-time pro's.
So, the term is not precise, either by feature, or function, but is at a price point that delivers great performance at a lesser price point than the obvious, so-called Professional bodies.
The R6 series is around the level of the 6D DSLR range as regards build but features are harder to compare because so many R-series bodies share the same sensor and focus / tracking systems in the new R- series. I think one clue is the inclusion of dual memory cards and battery grips, along with build quality.
I am a retired professional, but while I don't get paid any more, I still prefer that level of gear. So, in the DSLR line I retain a 5DsR, and an 80D, while in the R series I shoot with the R5 and both the R6 and R6MkII. They are all great cameras, and I would be happy to use them professionally.
As regards your questions... Only the R3, at the moment has a stacked sensor. That may change with the eventual release of an R5MkII and almost certainly with the R1. So, those professional cameras are not named for their sensor configuration, as such.
In many respects the big difference between the performance of the R5 and R6 variants is sensor size. The R5 has a 45MP sensor, while the R6 has a 20MP and the R6MkII a 24MP unit. That would tend to suggest that the R5 is all-round a better camera. Yet, in tests I have checked and my own experience the R6 has a 1EV dynamic range advantage over the R5: almost certainly because of its larger photosites. The R6MkII has retained that but has also other improvements with its newer design sensor. It is interesting to note that the R8 has the same 24MP sensor, but would not be considered a Prosumer camera because of its build, no IBIS and smaller battery, no dual cards. Whether a professional would prefer an R6 version over the R5 is not only for price, but what will be produced. For large, detailed images the larger sensor is obviously better, but if one is creating for social media or digital display an R6 variant may actually be better for both its price and DR performance.
I hope this is not even more confusing!
cheers, TREVOR
"The Amount of Misery expands to fill the space available"
"All the variety, all the charm, all the beauty of life is made up of light and shadow", Leo Tolstoy;
"Skill in photography is acquired by practice and not by purchase" Percy W. Harris
