Agreed, WiGEs are going to be fantastic for rapid-deployment, but that only comes up in A) Ridiculously large mapsheet games, and B) Tactical warfare, (which doesn't get used all *that* often).
Not that you aren't making a good point, because you are. I'm just speaking from a "forces already deployed and meeting in the field" standpoint, and from that standpoint I think the Ontos, or LRM carrier- or other long-ranged, well armoured, slow doodad- is going to be cheaper than the WiGE and equally good at controlling an open battlefield. Even if the WiGEs close the range fast, a staggered formation of Ontos means that they can support each other, and unless the WiGE's are stopping, they're going to *open* the range pretty fast too- then they catch 60 LRMs in the rear armour.
*pop.*
Edit- This does assume BV balancing, in a "ground-combat" scale game, rather than "tactical." Also, removed nonsense.