He didn't move (nor did she) as if she had hit him with solid blades that bounced off the armour - where against the spear they were fairly solid.
Not sure your point here - if you shoot a hose at a steel plate for long enough it might eventually bore through but you will never be able to use the stream of water to hang hang off the hole you bore.Secondly, solid is a state of matter, the same as plasma. Nothing makes a lightsaber "go solid", it just eventually encounters resistance such that it cant pass through. If i shoot a hose at a steel plate, the water doesnt "become solid" when it bounces off, it just cant keep going the way its going. We see in The Phantom Menace that dense/thick/massive enough material can provide some resistance to lightsabers.
In The Phantom Menace they push the lightsaber in and turn it - I take this to be working like a plasma cutter but it is debatable.