I flew with my six month old a while back with no issues. Gave her a bottle on both the ascent and the descent so her ears would pop and that worked perfectly.

She slept like a baby for most of the 5 hour flight and only cried once for maybe 60 seconds when she got hungry and I had to prep a bottle.

It definitely didn't seem like "babies experience a lot of pain" holds true at all if you plan for it