G,
I will say that I do applaud the look at the tech tree. I have my own feelings and concerns about it, but its one where I would be willing to try a beta of it to see how it feels.
The sword and cat changes I feel like I have enough experience with them that I know how these changes will go. My view, which has been echoed by several others, is that Swords already have an anti-infantry role in taking out spearmen. They currently already have a 59% stronger CS than a spear, that's a lot! Ultimately its not melee attacks that do swords in, its the ranged ones. If you have a line of spears and I have swords, than I will crush you. You have a line of archers with good terrain, and I'm in trouble. Swords don't take a lot of damage from archers, but it doesn't take a lot of damage to get into the vulnerable position where you have to retreat or risking losing a critical early unit to AI focus fire. In other words, its not the first volley that's the problem, the sword can take it. Its the threat of the second volley, which forces me to run my sword....which means that I effectively lost a unit for a good portion of time, and in early wars those few turns can mean a lot.
That's why I noted the Cover idea as a way to give swords even more defense against those threats.
For cats, I agree with others that iron is too precious, and cats too important. It will simply mean that instead of swords, I'll build cats. If you do want to weaken cats you can further increase the penalty against land units, so they aren't just your ranged unit substitute. But we have tried that in the past and its always been a flip flop. On the one hand you don't want cats to be dominant, but on the other your hammers are precious at that point in the game, and you can't expect the same level of combined arms where I have every unit for every niche represented that early in the game. I will also close this note that I don't agree with Tercio/Cannon transition as an issue that this change fixes. In my experience, the AI has 0 issues with this, because they tend to upgrade their units very quickly after getting techs. So the longswords upgrade to Tercios, and their iron is freed for the cannons.
As far as ideas for Spears and Pikes....what if you gave them overrun by default? So by themselves, they aren't very strong (could even consider a CS nerf). But with support, suddenly their CS power explodes, and they do extra damage when they kill units through the splash hit. This can represent the power of lines of cheap mass units...individually weak, but together get incredibly strong.