I've been a bike mechanic for a decade working on mid-to-high end bikes new, and working on all levels and ages of bikes old. I will say I came into this profession preferring the older stuff, but oh my god have things improved in every conceivable way on modern bikes. Not EVERYTHING is to my liking, but the modern geometry on a lot of the steel touring and gravel bikes is designed for an actual human being unlike bikes of old. The ride quality is amazing, which is nothing new, but many new bikes ride like butter, especially when you add things like a tubeless setup and some nice cushy tires. A good set of hydraulic disc brakes or even V-brakes will stop on a dime whereas many older caliper brakes are merely a suggestion.
Now if we are talking strictly high end aluminum or carbon bikes, yeah the durability may not be up there if you're used to the absolute 50-pounds tanks like older Schwinns, etc, but performance-oriented riders who are paying $3000+ for a performance bike don't want that either. If you're in the industry long enough, you'll see which bikes are "for you" and which ones arent. There are way more flavors today than there were even in 1990. If you like the older steel bikes, there are many modern bikes that will float your boat. The setup for a lot of this stuff is really not that much different than setting a bike up in the early 90s aside from weird one-off stupid designs from Shimano that only last a single model year or two. At the moment most of the current generation stuff is great despite some design duds in the past few years. In my decade of working at the shop we have only had to warranty maybe 1 or 2 frames for failures, both of which were approaching 15-20 years. The durability is not anything to worry about.
The only real complaints I have are some of the notoriously bad designs where they take a decades-old existing, reliable standard and try to overhaul it for...reasons. But the designs require precise tolerances that can't be met by basic inexpensive production methods. Stuff like BB30 for example was the bane of my existence for a while. Thankfully we have sales reps who we can complain to and even if they do damage control and act like nothings wrong, we tend to see those stupid technologies go the way of the dodo within about 5 years once they can't hide their mistakes any longer. Cannondale for example have returned to good old fashioned english threaded bottom brackets on a lot of their formerly-pressfit bikes. Thank god.
A lot of engineering goes into making the new systems shift without error, and smoothly, which is something that certainly not be said about any derailleur bike prior to maybe 1989 or so. And all that technology has trickled down so even the low-end bikes have systems with millions of dollars of R&D that have been borrowed. If anything even the cheapest bikes are miles ahead than the department store bikes of old....as long as an actual shop goes through and assembles and adjusts them correctly. Realistically the stuff isn't hard to set up at all, but you have to be sure of certain things...smooth moving cables, straight derailleur hangers etc. Nothing new either...
Now I'm a car guy, and I HATE modern cars. Completely. The technology, the hand-holding, the bulkiness, etc. But remember that they are absolutely perfect for the modern consumer. That's what they want. I want a thing I can fix on the side of the road with a screwdriver and an adjustable wrench. They want a thing that never ever breaks in the 10 years they keep it before selling it. There's an element of that in any transportation industry and bicycles are no different, except I've really come to appreciate the improvements since they are still (mostly) fully mechanical machines that can be fixed with simple tools no matter how much money has been pumped into the technology. The hydraulic stuff is a bit of an exception, and don't even get me started on the electronic shifting systems....but you don't have to have that stuff if you dont want it. Yet.
Stick around for a while and you'll go from being the guy at the shop who hates setting up disc brakes to the guy at the shop who can dial them in in less than a minute. Trust me. Practice makes perfect.
On many things right? How much do you actually ride high miles on your new gear? Most don't. How much to you weigh? Do you abuse in any way your bike off jumps or crashes alot then complain you broke your frame or crankset? Why? You can't expect it to not be affected.
