As someone with a professional cert in data center and telco design - This absolutely is a building designed for it, and no you cannot build it smaller. Everything about a data center is managing heat - servers can only be so close together because of the heat they generate, so you have spaced hot and cold aisles to allow convection to work. Server racks are spaced the way they are, and take up the space they take up, because the closer they are the localized heat is too much to handle - air is pretty bad as a conductor.
That site is also 1) New England's only carrier hotel, 2) a tier 4 facility (meaning ≥99.995% availability - which translates into less than 15 minutes down every 5 years), and 3) is designed for up to 40MW of power (It currently operates at 30MW) - all of which is backed up by onsite generators. It has something like 8 separate 13.8kV feeds from multiple substations, along different routings. That building has redundant everything - I believe it has 2N everything except cooling, which is N+1, simply because they don't have the space for it. 30MW of electricity going into servers generates enough heat to boil a thousand gallons of water every hour. The reality is that you can only put so much heat back into the air, and you need every inch of exposed area possible to accomplish that - and account for the additional needs of generators, some of which will be momentum UPSs, but the rest will be diesel fueled. Side venting through a mechanical floor does not move enough air. And once you get tall, you run into the problem of weight. Unless you can find a use for that waste heat, it's a nonstarter. I'm aware of some concepts, but none that have been built anywhere to my knowledge.
The fact is, that facility predates 9/11. Modern security requirements for a building like this with critical uptime look more like those for a federal agency headquarters - setbacks, fences and guards, and typically in no event do they include mixed use facilities. I can think of 2 in the US, This Macy's, and the former Verizon Building in NYC, where while the data center occupies the lower 14 floors, it has approximately a quarter of the capacity of 1 Summer. Large floor plates are a more efficient use of space for data centers because of thermodynamics and the redundancies involved - it's why the hyperscalers build million square foot campuses.