I don't really think you are speaking from experience here, GOF, just conjecture. You would be surprised at how well you can keep a Shield between yourself and your opponents weapon. Now if the Rapier user was using some "feint" skill and the Shield holder wasn't real experienced...then sure... But all things being equal... you are giving more to the rapier than Exists in reality.
I'm speaking from SCA experience, not live steel experience, which I'll grant does change things. A shield tends to have a lot of mass for its size, and once you get past shoulder-to-waist size, shield defense involves moving the person behind the shield as much as moving the shield in front of the person. Inertia is not your friend when it comes to shields. It's simple physics. If a person tries to work a 10 lb. shield as actively as his opponent works a 2 lb. rapier, he's going to wear his arm out quickly.
As for the spear, you can parry and strike with more than the tip, but: 1) one handed, it's medium slow (that inertia thing again), and 2) while you can put a lump on my head with the shaft of a spear, you can't knock me down or out with it, not one handed. So once I'm closer to you than the end of your own spear, if I'm willing to take a thump to the head you are DONE. Yes, in a combat to the death I'll take a bell ringing in trade for putting four inches with the point into your chest. I have a headache, but you aren't getting up anymore.
Parrying with a rapier isn't about BLOCKING a blow, it's about redirecting it. The broadsword wouldn't be too bad, the two-hander would be tougher and the axe would likely pose a bigger problem than the other two.
Exactly. See the final fight scene between Tim Roth and Liam Neeson in
Rob Roy as a good example. It's one of the only movie fight scenes I've ever seen that had all the SCA rapier fighters I knew saying, "Yeah that,
that's how it's done!" True, Roth's sword isn't an actual rapier, but it's light enough compared to Neeson's basket-hilt claymore that if he'd tried a direct block, he'd be holding a broken blade.
A Spear used in one on one combat is Used Much differently than in a Phalanx rank. Don't confuse the two.
Yes, but most of its effectiveness relies on being able to use both hands on it. If you have a shield in the off hand, that isn't one of your options.