>>714828615The T-60 didn't even need to be pre-war. It could have been explained away logically as the WC Brotherhood upgrading their T-45 fleet with the remnants of Enclave tech from the destroyed Adams Air Force Base. Forcing it into the pre-war setting was just asinine. Fallout 4 is rife with these lore and story tidbits that are like 1-2 sentences away from being perfectly logical, but instead are written in a really fucking stupid manner.
Likewise, the primary reason the Brotherhood should have despised the Institute is, after you steal data with the holotape and find out what they're working on, the Brotherhood discovers extensive research by the Institute into FEV, and that they're the ones responsible for the endless super mutants everywhere. But no, this is never brought up in the context of a conflict.