Isn't this the same thing? Meaningful is highly personal & contextual, so a problem that matters IMO definitely is meaningful.
Being good at something valaueable that you enjoy is one of the key measures of a life well lived for me, so kudos on that.
Finding meaning in your job doesn't mean that you have to accept terrible pay and long hours. It just means that you've put thought into what you'd like to get out of your career besides a salary. It's possible to find a realistic middle ground between fulfillment and max salary.
Because everyone spends the better part of their day at work, performing work that has no meaning to you comes at huge cost. You will never recover that time.
Personally, I figured I had enough to be comfortable and would rather spend my limited time optimizing things other than my W2. My last career move was an 80% pay cut. In retirement, I would do similar work according to my interests, so why not cut to the chase?
On the other hand, working for an ad-tech company and increasing revenue by 40% through some machine learning would have impact (on the company, clients, users, etc.) but not be particularly meaningful.
Just my own anecdata though.
Ad tech is a second order business. You're helping other businesses fulfill their purpose. I don't blame you for not finding a connection to value there, but that doesn't mean you can't find one in traditional industry.