Why not use a Combat Group
I read a book called Breaking the Phalanx and its update Transformation Under Fire, both by a retired colonel named Douglas Macgregor.
In his book we should concentrate on Combat Groups instead of the division as the all arms formation. The Combat Group according to him is smaller than a division but larger than a brigade. The current modularity going on in the Army right now is kinda based on it but rather a bastardization of the original concept. His approach to TANK/MECH is this.
1 Recon Battalion (Ground and Air (UAV) recon)
3 Combined Arms Heavy Battalions each with
--- 2 Tank Companies
--- 2 Mech Companies
--- 1 Engineer Company
--- 1 HHC
1 Strike Battalion (Artillery and UAVs with missiles)
1 Support Battalion (with improved support capability)
1 C4I Battalion (HQ, Staff, and other support like MP, ADA, etc.)
Total troops is about 5,000 to 5,500 and under the command of a Brigadier General.
As I mentioned before these are not part of a division but rather semi-independent. This semi-independent nature can be used to build a Task Force enabling a wider span of control.
This systems has it all, in my opinion. What do you think?