In fact, the idea that a knight in full plate had difficulty getting up, walking, or mounting is...you guessed it. A myth.
A "harness" of plate was heavy, yes, but it was also, if correctly fitted, perfectly easy to move around in. Pictures show that knights in armor could easily mount, from the ground (their horses were shorter, too), perhaps with somebody holding the stirrup. Replica suits have been made and in a properly fitted suit, yup, you can mount, dismount, run, or whatever you need to do. Riding armor, incidentally, leaves the insides of the legs unprotected so that the knight could still properly cue the horse.
Where the myth comes from is tournament armor, which was designed to take being hit by a lance and was also built to make it harder to fall off the horse. This armor did reduce a knight's mobility and unhorsed knights at tournaments often needed their squire to come help them get up. Tournament knights would mount from a block or get a leg up, just the same as with modern people who can't quite manage to mount from the ground.
So, no cranes. Indeed, no excessive difficulty at all.
Modern knights demonstrate the art of jousting at Hever Castle in Kent. Image source: Peter Trimming via Wikimedia Commons.