Honestly speaking the problem wasn’t the mothership core at the time, it was the combination of Adept-Oracle basically being game ending since you couldn’t deal with both the adepts and the oracle simultaneously. Not with any real regularity or consistency.
In theory cyclones were the only real answer to it, but in practice it was… not anywhere nearly as effective.
Which is specifically why I’m not opposed to the removal of liberator circles giving additional vision, but also simultaneously further reducing their vision on top of that is frankly, very stupid.
While it does come out somewhat early, it’s not much earlier than say, a tempest rush (which is abusive as hell in its own right), and every race has the ability to deal with base range liberators with reasonable efficiency. Zerg has both queens and moveable spores, and Protoss has stalkers, Phoenixes and Void-rays.
Liberators aren’t cheap early game (granted, not as expensive as a tempest, but still), and its range is far more limited than any other siege unit in the game due to the nature of it only being able to target within the circle.