Honestly I can't imagine how that could be effective. I mean, the heat of battle, you see a fast moving guy. "Oh, he's gonna attack me, I better switch to my sword". Agi guy runs past you. "Oh he's not, where is my steel pick...".
Carrying additional 1.7 kg just for an arguable advantage of reach in some very limited cases doesn't seem worthy to me.
You'd want to have some more use of a weapon you have to carry with you all the time (like horse rearing in case of spears).
Two questions for ya:
1. What are you smoking?
2. Why are you not sharing?
You already got a 5+ weight shield slowing your ass down, so that 1.7 extra weight doesn't really matter unless you are high agi, super runner. And while a spear is nice against cav, a nice long (arming) sword is almost just as good, especially if you don't have pole wpf (or, you can just, like, jump to the side and dodge 99% of incoming cav).
You don't switch weapon as someone is attacking you, but if you start fighting and you realize/recognize that the enemy will just hold S key all day long, together with some kicks, you can just take a step back and safely switch. If you are in a situation where switching weapons will give the enemy a free hit, you are also in a situation where you're short weapon is also inside range of him. Or if all fails, jump, backpedal yourself or shove the enemy away and then switch.
