I wouldn’t completely rule that idea out if I felt I had a compelling argument. I assume it’s going to be tough to produce data on how widespread this issue is.
Warning: really long post!
I doubt that this type of case would ever be compelling (i.e. highly likely that you will win), however you might only need one individual to see things your way, depending on exactly how small claims court works in your state. In my state, SCC is nothing more than a claim by one party against another, heard and decided only by a judge, with no lawyers taking part in the proceedings, and with a claim cap of $6K. Of course, your state might have different rules, which may or may not work in your favor.
Now AFA as how widespread the NA cracked head issue is, there are 2 significant sources of information that I'm aware of. The first one, which you already mentioned, is the NHTSA complaint website. Although there are very few cracked head complaints from M3 owners, there is what I consider to be a considerable number of them on the CX-5 side. At last count, I found 26 NA cracked head complaints for MY2018, and 20 for the 2019 (with that number steadily increasing in the recent past). Now those superficially do not seem like huge numbers, when compared to the total number of CX-5 vehicles sold. However, very few owners are aware of this complaint website and would know anything about filing a complaint there. Secondly, the overwhelming number of cracked heads were repaired under warranty, and very few individuals are going to file a complaint for a repair that was done at no cost to them. IMO, anyone who is familiar with the history of how this complaint site works, would consider those cracked head numbers to be very high.
Setting the NHTSA complaints aside, IMO the most significant source of information on NA cracked heads is the Facebook CX-5 Group (the North American CX-5 group, not the European one). First off about me and that group, I'm an old dog who has no interest whatsoever in the world of social media. That said, I did join this group, and follow along very closely as a reader. Lots of other people comment, so I don't feel the need to participate. I can say for certain that this FB CX-5 group is by far the best source of 'inside' information related to the NA cracked head issue.
The primary reason for this being such a valuable resource is the multiple Mazda techs who have shared some of their NA cracked head experiences and history, including a few who have provided an estimated number of repairs they have done. I believe that all of what they've posted on this group is 99.99% reliable and honest. These are not disgruntled employees, just regular people who have chosen to share information in an off-the-cuff manner. And it's also information which I'm certain the automaker would very much prefer was not communicated to the public.
The other source of information from this FB group is the fairly numerous long threads containing reports from various owner/members, describing their own cracked head experience. Although a few of these owner reports might not be completely honest or accurate, for the most part the fact that the source is a named individual, would tend to validate the report (yes, I'm aware that fake accounts do exist on FB). You will also find many comments from individuals who downplay this NA cracked head issue. My only response to that is that there are always going to be people who are very willing to give offhand opinions, without doing any real research on the subject they're talking about.
So, if you're willing to invest some number of hours to carefully comb through all of the cracked head threads (conversations) of this FB group, I believe you will arrive at the conclusion that the NA cracked head issue on the early year CD CX-5 has been massive, particularly with the 2018 (which was not installed on the 2018 M3). One very significant drawback with FB is that they 'hide' many posts, which forces you constantly need to expand the 'additional reply' links manually as you read through the content. This 'feature' makes this research process very tedious, because you need to make sure you expand every hidden post and read through all of that content as well. And many of the most important posts are 'buried' this way, so you need to go very slow, in order to not miss anything. It can become extremely frustrating to have to do this repeatedly, however the end result for you may very well be worth all of the annoying journey.
So if you think this is something you might want to consider doing, I recommend immediately capturing all of the content that you would want to submit with your case. Do that as you go, because you definitely would never want to go through all of that stuff a second time. Just search for 'cracked head' and 'cracked cylinder head', and concentrate on the ones which have been posted within the past year or so (where the most useful information is). And if you do this, make sure to indicate anything from a Mazda tech, because IMO those comments carry much more weight than anything from an owner. I'd also keep it as concise as possible, while at the same time presenting every meaningful post that you can find, which adds additional support of this being a widespread issue.
I believe that if you build a solid, well-organized collection of information from both this FB group, and also all of the NHTSA complaints, it might very well have the desired effect on any given judge, particularly if he/she has some bias towards the consumer, instead of the business. Your claim would be that NA cracked heads on the early CD engines is a systemic issue, and that the consumer should not have to take such a significant financial hit when the automaker messes up so badly.
And there is one other important consideration related to collecting all of this information. It would be very interesting to find out what Mazda Corporate's reaction would be, if you sent them a copy of what you've prepared, and are planning to use against them in SCC. Who knows, perhaps they might just cave on the spot, and prefer to pick up most or even all of your tab, rather than have all of that negativity show up in a place that's available to the general public.
If it sounds like I've spent quite a bit of time thinking about this, that's because all of this is exactly what I'm going to do myself, should the need arise at any time in the future.