Even with today’s technology, Mazda simply can’t overcome these flaws inherent from the cylinder deactivation.
Actually that's more a theory than practical application. I hate to sound like a broken record but Consumer Reports reliability ratings, based on owner reports from their four million members do not bear out your contention. Time will tell, but there is little evidence to support your claim.
In CR's engine-major category, all CX-5 years from 2019 forward have the highest rating. 2018 has been downgraded over time to average. That rating may be related to the CD rocker arm / stall recall, which the PCM update appears to have resolved. Or it could be turbo related since CR reliability ratings are aggregated across all trims for any particular model year. If the 2018 rating is related to the recall, then it is just another in a long list of cautionary tales regarding buying the first year of a model, generation or significant powertrain change regardless of who makes the vehicle.
That said, the TSB below raises some questions but since no specific problem is identified the mods to the cylinder head assembly could be for any number of reasons not related to longevity.
Back to CR, engine-minor ratings score the highest reliability rating for all years since 2018 except for 2019 which is down one notch to 4 out of 5.
Frankly, you'd be more likely to encounter problems with in-car electronics (endemic in the industry) or power equipment as the ratings in those categories yo-yo up and down over the years, or gen 1 brakes, or 2013 electrical systems.
There's probably 500,000+ CD engines on US roads. Perhaps more since Mazda does not break down sales by powertrain. Do we have to reiterate that anecdotal issue reports on a message board are not the best way to assess reliability? Only time will tell, not theories about a Mazda theory.
Frankly, I'd be concerned more about buying any new vehicle from anybody produced since the pandemic supply chain issues took hold. With the possibility of production line work flow being reorganized with part supply interruptions, "moving the cheese" in the assembly process opens up all kinds of potential assembly flaws.