This. Corporate work in particular tends to make people stupid. The 98% who don't climb the ladder end up associating what they are (or used to be) good at with subordination and failure, while the other 2% have optimized themsleves to appeal to stupid people and end up just like the set of people (executive blockheads) they're trying to join.
People who protect their intelligence and creativity, damn the consequences, tend to keep them for a long time. People who buy in to the corporate system turn into morons. The problem is that they don't notice it happening, and that, as one gets older, it gets harder to recover.
The person probably meant they didn't really get to coast and just do the same thing over and over again. Many kinds of mundane-looking corporate work are often hard work.
You think getting certificates is improving your mind?
My experience in corporate work is exactly as the comment you replied to. Endless drone work doing much the same things day after day. I did it for 3 years, learned basically nothing beyond what I came in the job with, then went out on my own. In the time since I have learned so much more than what I did in that corporate job, there is just no comparison. Also, I strongly suspect they literally try to keep you stuck in one spot and too dumb to move out of it on purpose; you are less likely to leave or ask for a raise. They want predictable drones in corporate work, and yes, getting certificates is one way you make drones feel like they are doing something.
I've worked for startups and for very large companies. I've also consulted for both, and dealt with executives and decision-makers in both spaces. And, respectfully, three whole years at one job is a drop in the bucket in terms of experiential breadth and making sweeping claims to the universe of corporate work from it is unwise. "Drones" "drones" "drones" is just look-down-your-nose silliness and while I am not a cheerleader for tech certs generally, I have a few in my background, and there's significant value both personally in the effort to better oneself and in the practical, learn-what-to-learn you can derive from them. (AWS certifications, for example, are pretty significant in terms of what-you-have-to-know when you get past Associate.) Even aside from that, there are tons of medium and large companies actively and consistently working to provide opportunities because internal transfers are (usually) cheaper and no less likely to succeed at new and more complex roles than hiring externally. Heck, even in places where that isn't necessarily a company focus, I've seen reading groups, SIGs, etc. form just because people want to learn new stuff. Tale as old as time.
One job, three years. Perhaps you had a bad job. But try this one on, too: perhaps you lacked the wisdom to recognize opportunities where they appeared, and you're better at it now.
If you don't want to do endless drone work (who would?!?) then why would you stay at that job?
I've never stayed at an unfulfilling job - how pointless. I've made a point to network outside my immediate group - and most importantly be nice as well as helpful to others. It really makes a difference; people notice. All of my jobs, including my current one, came to me based on my reputation. There was no luck involved, just honesty and steady work. I won't even say hard work because it was always work I enjoyed.
People who protect their intelligence and creativity, damn the consequences, tend to keep them for a long time. People who buy in to the corporate system turn into morons. The problem is that they don't notice it happening, and that, as one gets older, it gets harder to recover.