Do you have to thumb a baitcaster?

[Jaderose]

Yes.  I can't speak for DC reels but for reels that don't have batteries (lol) it doesn't matter what kind of line you have, you have to have an educated thumb to use that reel.  Most of my reels have "Dual Braking Systems".  I keep 2 of the centrifugal brakes on to help at the beginniing of the cast but have the mags turned basically off and the tension control knob turned to free fall.  My thumb IS my brake.  Once you get muscle memory, it happens automatically.  I couldn't stop doing it now if I tried.

[Fishes in trees]

The short answer is yes.   For a longer answer you can research  into the details of setting your brakes and cast control knob, which very some from reel brand to reel brand and at the end of the day the answer is still yes.

[Bankbeater]

I was taught never to trust the tension knob, or the breaks on the reel.  Always use your thumb.