Still exams, so no time to really type out arguments and support them with proof and examples. However, a few points:
-tanks can be much more armored than battlesuits while retaining mobility, because tracks take the load better. Proof: lift and carry something, then put that weight on a skateboard and push it. Which is easiest? If we use tanks, they should be able to tank (pun unintended) gauss cannon rounds with ease.
-I have always said that battlesuits are not the replacement for tanks. They are heavy infantry support weapons, designed to bridge the gap between infantry and armored vehicles. This is important, because yes, they might be better in small corridors and tight urban settings (just like regular infantry) but they rapidly lose out in other engagement types. Such as medium range, or open ground. And who says all our (as in, ARM as a whole) battles will be at close range?
-yes, the UWM doesn't really need tanks in it's current wars. Which is exactly what I said: they don't need them in the type of conflicts they have. But we, ARM, will be fighting a different kind of war, than the UWM has been fighting for a while now, so it could be that conventional armored vehicles find their use again. Why should we fight this war on their terms, or only use the kind of weapons they have?
-tanks are faster than battlesuits. Go fill a backpack with rocks and run with it, then do the same with your bike. And tanks divide their weight much better, so they can navigate soft terrain better. That's just physics again.
-you severely overestimate the ability to dodge a shot. Ask a friend to throw tennisballs at you, how good can you dodge that? And even if you use computers to circumvent slow brains, legs are still bad at quickly jumping about to dodge bullets (you need to bend the knee and push off before you even begin moving. The second wheels start turning though, they vehicle moves). Unless you just throw yourself to the ground, which might work.
And if you say 'they could dodge if at medium range or further' I must point out that tanks are better at medium range or higher, a least when using real-ish physics.
-why would the tanks be 'lumbering'? If ER tech is good enough to gave multi-ton legged vehicles with acceptable speed and agility, wouldn't conventional tech also increase to the point you have a speedy, agile tank?
-in real life, there are already armored vehicles designed to be used in urban settings. For example:
http://en.m.wikipedia.org/wiki/BMPT