Yes, of course you are correct in many senses. But I'm hard pressed to think of a field that hasn't seen tremendous change in just the time I've been working professionally let alone my lifetime! Even the art of cuisine has changed so much that some chefs I know are struggling to keep up late in their careers - it seems like all the top chefs are new and almost impossibly young. It really used to be that you could learn your skill, unchanged from your teacher, and do it for your entire natural life, passing it along to your proteges who would then do that same skill exactly the same for their entire lives.

So while I'm pretty sure the basic physics you use is largely unchanged, I'd bet that a mechanical engineer for even a generations ago would have trouble recognizing much of what you're doing today. We have materials, measures, testing and production methods available to us today that would have looked like magic to somebody in the 60s. It's like comparing a flint-lock musket to a modern rifle. A gunsmith from the flint-lock era would know the basics, but his expertise would be obsolete.

Even in software, most of what I learned in my undergrad CS program has stayed refreshingly relevant, but the act of writing software itself has completely transformed a half dozen times since I graduated. It means I can sit down in a new environment and learn the syntax, practices and idioms of a language and dev environment relatively quickly. But in many cases you quickly start to feel like you're treading water at the same time, having not 20 years of experience but risk having 1 year of experience 20 times unless you carefully cultivate your expertise to prevent that.

My civil engineering friends seem to have similar feelings, lots of the physics and basics they learned are still relevant, but the theory and implementation, especially the huge changes in Urban planning are having tremendous impact on their ability to cultivate expertise.

I have a landscape architect friend who graduated hoping to design golf courses and parks and who now spends most of his time working on energy efficient certifications (LEED) and planning for new construction and retrofits. Something that didn't even exist when he entered his line of work. Instead of becoming an expert in park design, he's become an expert in LEED certification.

Even my pastry chef friend left pastry school, where she intended to make traditional French pastries, and entered a world expecting innovative techniques and ingredients catering to the allergen/wheat sensitive/low carb/vegan/no GE/whatever crowd of the month. She doesn't just make scones, she has to make 6 kinds of each scone suitable for everybody's special dietary decision.

You're right in that they're all still doing mechanical physics, looking at water management, and baking things in an oven. Expertise in those subjects transcends. But being an expert in their fields is impossible because the expression of what their entire fields are are being redefined almost every day. What they're becoming experts in, and something their predecessors didn't have to do, is riding the wave of change.

This is a fundamentally different kind of expertise that maybe only ever existed in human history during times of war, or great societal upheaval. "May you live in interesting times" is a curse, not a blessing. It's to be seen if this is simply the new state of things from now on or a time of upheaval that we can't recognize and things will settle down at the other end.