It was probably necessary, the only other options would have been to continue with the VM-T which the soviets were using for the same task on smaller space part

It was probably necessary, the only other options would have been to continue with the VM-T which the soviets were using for the same task on smaller space parts, or the An-124. The VM-T would have been underpowered for the Buran, it was really used to carrying smaller parts and only had a payload of 50,000Kg (1/5 of the An-225, and only slightly higher than the 42,000Kg of the Buran orbiter). The An-124 on the other hand was too short, even though it had adequate payload capacity. So the An-124 would have been needed to be extensively modified to carry the Buran anyway. They may have over-engineered it somewhat, but then better to over-engineer than under-engineer and end up with an embarassing accident. The 747-100 that Nasa chose to use for the SCA didn't need quite as much modification to make it usable, and had a fairly high payload rating anyway (around 170,000Kg), and was long enough to carry the shuttle.