Subban had a developed offensive game when drafted, in his D+1, and in his D+2. He absolutely was not sent to Hamilton to learn more offence.
He was drafted 45th and not 5th because of defensive awareness issues and he needed to work on them.
Even after he came up, he got benched and even scratched (rarely) in the next 1.5 years due to defensive concerns that would flare up. But the issues were ultimately minor enough that we was easily in our top 6 overall by the end of 2011, and climbing.
Pacioretty was sent down because, for whatever reason, his results were not good enough to stay in the starting lineup. At age 21, he scored 3 goals in 52 NHL games. That being said, had MSL been coaching with the approach he is using now, instead of Jacques Martin who was trying to win a Cup, it might not have been necessary. We will never know.