How are halflings going to make up for 2 less offense on their specs compared to UD elites? Assuming 90 opa Halflings need to have 4 extra space to fit them in.

Yes they have 2.5 extra pop from their racial bonus, and they need some less thieves, but still you're not getting quite there. Besides, UD have secondary bonusses like lower off losses/plague. Halflings will need to run high hosps if they want to be successful. Also, halfling offense will be very susceptible to NS/propaganda (when caught home).

Also the BR will kill you in war if you can't kidnapp. I'd say halfers need at least some tpa to be effective and not run out of pezzies, but then you're not going to get more than 65-70 opa. Orcs/UDs with the right build can easily go 120-130 opa.