I could never be forced to have my carry-on checked in, and was allowed to take my bag under the front seat for the simple reason that it contains several items that either should not be or are not allowed in cargo: laptop, medicine, powerbank, eyeglasses, house keys, wallet, book to read in flight and so on. I kindly ask them for a plastic bag about the size of half of my carry-on bag for these indispensables, and that closes the case.

Hi! I'd like to contribute to this discussion by suggesting that you
might be optimizing the wrong thing. In my experience, both airports
and airplanes actively work against you having quality time with yourself.
Let me explain, based on my Western European travel experience.

Airport seating is seldom comfortable: you typically get slightly reclined
seats, and benches where you could lie down simply don't exist.  Try
holding a laptop or book in a working position while reclining: it
requires constant effort. These spaces aren't designed as desks for
intellectual work.

The acoustic environment is challenging too. You get essential boarding
announcements mixed with routine safety reminders, and since they sound
similar, you need to actively listen to each one to determine whether
it means you'll miss your flight or simply that you shouldn't leave
your bag unattended (which no one does anyway: theft is not unheard of).

The visual environment is equally overwhelming. The last airport I visited
was dimly lit: just bright enough to read. It featured huge, blazing
advertisement screens.  The shop displays are also harshly lit, constantly
pulling your attention away from any book or laptop.

If you survive this ordeal and board the plane, it's more of the same.
Modern seat pitch doesn't allow you to unfold a laptop properly, and
the tray table is so shallow that even a book barely fits at a comfortable
reading angle. The seat width is such that an average-sized male shoulder
width barely fits, leaving no space for adjacent passengers to place
their arms. Someone inevitably has to keep their hands in their lap.

Then there's airplane food: mostly expensive junk food that I wouldn't
recommend unless you have an iron stomach and very low standards.

Time isn't really the issue here. The real question is how to reach your
destination without being completely drained. There aren't many solutions,
but when available, I'd suggest using quiet airport areas and choosing
flights with reasonable seating or selecting better seats. Both are
increasingly rare these days. If you're fortunate enough to find them,
you might actually have a pleasant, slow journey. Otherwise, which is
usually the case, no matter how you optimize your time, the travel
experience will leave you drained and irritated.