Long reply... get comfortable.
I disagree with a few concepts and conclusions.
My least favorite thing about the article is that he spends the whole first half of the article intentionally making alarmist statements. These parts of this article sound like they were written by a 70+ year old guy who's lost his mojo and stuck on old thinking. My eye was twitching the whole time and I didn't even want to finish the article... I've heard this music before.
Intro and "how we got here"
All this talk about Reach without ever once mentioning STA, Stack, stem length, handlebar width, front center, rear center, etc. Only mentions BB height a couple of times (which in some cases isn't that different today).
With modern bikes the Reach gets longer, stem gets shorter. All for the better! Instead of long stems and narrow handlebars where you turn your whole upper body with the handlebars (ish), the stem is shorter and your hands are now in-line with the steering axis of the fork. Mountain bikers across the board seem to like this setup.
Serious question: If we knew more about geometry at the time, instead of making a knobby tired bike with road bike geometry, what would a 90's MTB with 26" wheels and rim brakes look like with "modern" thinking in the geometry department?
Serious question #2: If McCormack had spent his 20+ year career working with "modern geometry" bikes, what would he think about 90's bike geometry and fit? Would the tables be turned?
Thankfully he finally got down to some relevant content in section two and three: "Fit failed MTBers" and "What's the solution".
Serious question #3: If you have the "wrong" tires, tire pressure, suspension setup, fit setup, etc. on your bike for your riding style
or local terrain that causes you to ride a certain way or prevents you from riding a certain way, could it impact your impression of the bike, fit, geometry, etc? Answer: yes.
What I don't get: He's talking about his current Ibis Ripley with SQ labs handlebars (to get the hand position in-line with the steering axis) and then says in technical slow speed terrain that a Small frame (he's 5'9") would handle better than his Medium. Is this just as dumb as saying you want to ride a XC bike to the top and a DH bike to the bottom? OK, so a shorter wheelbase that's more maneuverable and lighter is better in slow speed tech?! Shocker. This DOES NOT mean your bike is too big for you. Let him jump on that Small and descend high speed chunk, or spend all day pedaling it on mixed terrain. How awesome is your Small now??
The last couple of sentences reference Richie Rude (pro Enduro racer) and how he's almost 6' tall and riding a Medium Yeti SB150. I'm not a fan of comparing the needs of pro XC, Enduro, or DH racers to average riders. There are so many variables and needs that apply to them that don't apply to the average trail rider. It's a terrible comparison in most cases, this one included.
Is your current bike too big?? NO. Where are all the forum threads of people complaining that their bike is too big? Was the standover clearance of your 90's bike terrible? Yes. Doesn't that mean that it was too big by modern thinking?
Personally I have come to realize that my old bikes were WAY too short in the Front Center department. The front wheel was way too close to me and I'd go OTB when going over a big log or down a steep technical feature. Thankfully that is a thing of the past.
Oh BTW I'm 6'3" and I've never ridden a bike that was too big.
Overall this is just typical big media style writing where it's more about click count than actual content or useful conclusions. There is some good info in there, and some of the conclusions may prove to be correct (time will tell), but I won't be clamoring to read his next article.
(I have many more thoughts on the subject but wanted to keep it short.

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