I spent three weeks on a Marinaut 21 on Lake Powell, and I have a C-Dory 22 myself (which I have used on Lake Powell). In my opinion, the comparison isn't really about "seaworthiness." Neither boat is a true offshore boat, neither has a self-draining cockpit, etc. That's not to say that can't go offshore, because they can, in calculated circumstances. And either boat can be "seaworthy" in the sense of "ship shape." A lot also depends on the captain and crew.
Here is where I noticed differences:
1) Basic hull shape. The concept is similar, but I think the Marinaut has a slightly more balanced, "magic carpet" ride. Also with more reserve buoyancy in the stern, you can run something like a Honda 115. The 22 these days is almost always a bit overloaded in the stern. It handles it beautifully, but it's still a slight factor (motors were lighter, fuel tanks smaller, battery banks smaller/lighter/etc. when the 22 was designed).
2) Certain details are a bit more refined. For example the stern cleats are located such that lines just naturally lead fairly off them, a fender there won't roll around the back of the boat, etc. You can hold onto the cabin-top handrail and reach for (and grab) the bow rail with no "air space" in between. The gunwales are wide enough to sit on. The fuel tanks are saddle tanks so you have more storage room aft in the cockpit. The cabin windows have slightly better sight lines (at least for me). Etc.
So why do I have a 22? Well, even though it's not quite as slick, it does the job beautifully. Also, I was content to buy a used boat, so the price was 1/3 to 1/2 (since you can't find a ten-year-old used Marinaut 21 yet). Maybe my boat is not as nice, but I have a hunk of cash left over to go boating with. This is of course an individual choice. I also think the 22 is a tad better looking. But if someone offered to hand me either a 22 or a Marinaut 21 for free, just pick one? I'd pick the Marinaut 21. Others may have other choices, and I LOVE my 22!
I think the Venture 23 has many of the same improvements, but for me the extra 1,000# of towing weight (over the 22), took it off my list.
Not sure how the 25/26 compare, as I don't have either of those.