Firstly, tanks have much heavier (better) armor, and a better profile. They
also have a better... angle of the armor? There's probably a better term for it, but if the armor is slanted, then most of the force of incoming rounds is deflected away. Additionally, they don't really have any weakpoints- just about everything can be heavily armored, with at worst small seams.
But a battlesuit always has a bad impact angle for the armor, and the flat section is right over the user. They also always have a weakness in the form of joints. For the dominion, I used the solution of putting avatar cloak over the joints, but that still won't hold up to sustained infantry fire. A battlesuit will
always be somewhat vulnerable to infantry fire.
As far as mobility and dodging... I hate to do this, but have you ever played one of those war simulation games, like ARMA? Tanks most certainly
can 'dodge' to the extent that anything can dodge high velocity projectile weapons. Namely, they can move fast (faster than a battlesuit), and they can turn and weave. And they can redirect their momentum faster.
A battlesuit, on the other hand, can't run as fast as a tank, and at full speed
can't turn as fast as one either. Have you ever driven a high performance sports car competitively? They can turn quite fast if the driver knows what he's doing. It can use cover, but how often is there actually cover that's really useful for a battlesuit, at least against the UWM's anti-tank equipment? Maybe stuff like 'instead of instant death, just lose most of your armor', but a battlesuit is already so armored that most cover doesn't mean much.
I will say that a battlesuit is better for MOUT, for all the obvious reasons. However, it's still limited enough that I'd rather have something like a
Dominion suit, so that it can go room-to-room.
As far as space magic: Well, if we use that argument, you do realize most of everything about strategy is thrown away, right? Space magic is so far above the power of conventional weapons for everything except mass slaughter, that if we were logical we'd equip our troops with nothing but. And make extra decomps with the savings from never making any con weps.
But I digress; there is a defense against space magic: automanipulators. Set one to keep an area at
exactly 98.6°. Set it to keep an area perfectly static in relation to the manip. Set it to make sure it stays at 1g. A particularly mentally strong space wizard can probably overpower this, but it is much harder than normal, and I bet you can further upsize the manip to make it even more difficult.
Automanips are better on tanks than battlesuits, primarily because tanks occupy a pretty consistently shaped space relative to itself. It's turret moves, but the main body is basically a box. It also has more power to carry more weight, which translates into a capability to carry a larger volume, which means it can carry bigger and stronger automanips.
A battlesuit on the other hand, has four limbs waving around. You can't defend those with automanips unless you defend a big sphere around the thing, which is a terrible idea. So only the cockpit can be defended while the limbs are ripped off. That's still pretty good, but at least the tank can still run away afterward.
Oh, and as mentioned before, a tank's better at dodging than a battlesuit. A mobility battlesuit is better than either though, and is pretty much just as resistant to infantry level weapons.
maybe someone should design a mobility battlesuit that trades size and armor for even more mobility, while retaining juuust enough armor to resist infantry. >.>Because I'm sure Sean'll mention it again: Yes, there are materials that we could research that would benefit a battlesuit, and not a tank. Don't you think there's materials that could benefit a tank but not a battlesuit? Or, hell, would benefit both, and would therefore be overall more useful? What makes those harder to research than the battlesuit one?
NOW. All of that has been said, so you'd think I support tanks over battlesuits, yes?
I don't. Because those arguments look at the problem realistically and logically, and the problem is an RTD set in the distant future with space magic, all run by an
english major. Those arguments are all in relevance to the grand war effort, while the only thing that this stuff will likely have any real effect on is our own actions. Therefore, our equipment should be specifically tailored to the engagement we actually get in, which do not include combined arms, do not include large scale battle, almost never include battle at ranges beyond 'close', almost never include non-urban battles, and almost never include things that are realistic but not fun (read, half of the preceding points).
We can still design tanks, sure, but we really shouldn't until all the things we'll actually use and need are done.
TL;DR: You're all wrong, except for the guy who's kinda right but for the wrong reasons.