Coffin corner isn't just a thing at 70,000ft in a U2, it applies to regular airliners at much lower altitudes as well. When heavy the maximum altitude for a normal passenger plane can be several thousand feet below it's certified maximum service ceiling.

What helps is that due to procedures nobody flies manually at such altitudes. So it's up to the autopilot to maintain a specific airspeed.

A similar effect exists at very heavy weight on takeoff, the gap between the stall speed and the maximum speed for the flaps can be as little as 20kt in a fully loaded 777. That requires good concentration and constant monitoring in the climb to not get a stall warning or a flap overspeed. This part is often flown manually.