You're right on all points of course, the larger SAK's are stronger and better cutting. Just like a full size service pistol is a better all around tool than a smaller caliber pocket pistol. But...it all depends on what you need. What I have found out in my later years is...that little penknife is all I need in my lifestyle as a mostly urban/susburban dweller going about my business in that surrounding. Putting all ego and fantasy use aside, this old curmudgeon just doesn't need much knife going about my modern suburban life, picking up the dry cleaning, going for a walk with the dog, fetching a carry out pizza for the wife and I to have while watching the TV at night.
Some people find they need a full size 5,000 pound SUV to feel good, while others find a compact car like a Honda Civic or Toyota Corolla just fine. All depends on your lifestyle and uses. I have a bigger SAK, the old Wenger SI, but it only gets carried a bit now and then. Mostly all I need is the 58mm. Just like I get by very well with a Toyota Corolla for my needs, to include a trip from Georgetown Texas to Mission Viejo California a couple times a year to visit with the daughter's family. I'm not a hunter so I don't need a hunting knife. I'm not traveling the wilderness anymore, so I don't need a bushcraft or survival knife. I do some gardening, but I have my Victorinox florist/garden knife for that on the pocket of my apron, along with pruning shears. I do a great deal of fishing in my retirement, but the little 58mm blade is just fine for monofilament fishing line. The little scissors are great for trimming off a knot with new hook on the line.
But most of all for this senior citizen with some arthritic fingers, the 58mm blade is just fine for slicing through all those plastic packages that are hard for a senior to open. Everything comes cocooned in plastic these days, and I find it so much easier to just take my little classic and slit the damm stuff and go on from there. Even sitting a bench in the town square by the old courthouse, the little classic gets no attention. In fact, it's so small, I doubt most people around even see it as it's mostly concealed in my hand for the art of stealth cutting that I practice in public. The classic has more than enough blade for this old codger to open the packages of snacks while sitting on the river bank waiting for bite, or a park bench in the town square.
It's all about who you are, where you are, and what you do. I got by for years with a little Case peanut for my pocket knife. I had no more use for the larger heavier Buck stockman I used to carry in my 20's and 30's. Just like I have no more real use for 4 and 5 layer SAK's in my life, while the 58mm does what I need in my later years. And the smaller items save enough weight and space that there's room left over for the stuff I now need to carry in those pockets. Some pain meds for the arthritis, eye drops for the dry eye that popped up in my 70's, pipe and pouch of tobacco for the quiet times on the river bank, a Bic lighter for said pipe, keyring with house and car keys, small AAA pocket flashlight for when it gets dark every night, small 5 shot revolver in side pocket for times that some young punk thinks this old fart will be an easy mark, note pad and pencil because at this age we need to make notes because we can't remember Jack S--t and Jack in on vacation in Vegas. Wallet with essential id, money, cards etc, bandana for whatever, small bag of mini milk bone dog snacks for the furry child that goes with us everywhere. Most of all, the RONCO pocket defibrillator in case of serious vapor lock.
There's just a lot of stuff that is more important than a larger knife that I don't really need. I'll save space where I can.