I don't own and never used/needed and could never justify the cost of a pro saw. All I have is a little Stihl MS170 with a 14" bar ($150 new). For the past eight years I cut 10 cords of firewood a year with it. It's been as reliable as dirt with ordinary (read "little") maintenance. Most of the trees I take are 18 inches or less, but have cut a few 24"+ trees. One year, I bought a full load (12 cords) of hardwood logs and bucked them all with that little 170. It's been a pure pleasure to use. It's done everything I've asked of it. Just bought a brand new MS290 Farm Boss with a 16" bar. I didn't "need" another saw. I just "wanted" another saw. What a difference ! Does this me I have CAD ??? Are pro saws "better"? Sure they are. That's what you're paying more for. A better saw.
Given its intended purpose, I think a home owner saw will last a very long time (with proper maintenance and use). But if I made my living with a saw, 8 hours a day, 5 days a week, I would probably get a pro saw. They both have their place. I just don't think a home owner "needs" a pro saw. But if they want one, more power to them. Pro saws can be a lighter, and that can make a big difference to some homeowners. Frankly, given all I've done with my very light 170, I can't see how a homeowner needs anything bigger than a 170, unless he cuts trees bigger than say 28". A friened bought a brand new Stihl 261 4 years ago. He's used it "once" to cut a few 8" lodge pole pines. He wasn't very good at it and asked me to finish the job for him. I keep telling him he should at least drain the gas out of it, but he never has. Just for the heck of it, he tried starting it this summer. No go. It probably ain't gonna get fixed either. (And "no", he won't sell it. I asked.)
Concerning longevity, I don't think there's been any definitive, objective, and quantifiable long term studies done. I think many of us have some very good longevity reports on what ever saw we use, be it pro or home owner. I calculate that I put around 30 hours a year on my 170 to cut 10 cords of firewood. (I'll be 66 this month and have only two speeds. Slow and slower.) I have a ton of saw time on my little 170. Just had the chain oiler replaced last week. Only thing that's been repaired on this saw. I expect the same reliability and longevity from my new MS290.
Don <><