Of course it made it big difference. There were people with dozens of accounts getting access to over 100Ds a day to do what they wanted - at least 1000 diamonds a week. This allowed them to create and buy equipment that anyone else, that is not doing this, would be unable to make. One guy that I know back when there were 15Ds a day per account was getting nearly 500Ds a day, nearly 3500 a week.
Thankfully they are getting rid of it.
Sort of sad to try to do anything this way. To start with you would have to have unlimited gold and time. Even with only 10 accounts you have to spend 8,000,000 gold ever day just to get 3 diamonds on each account. At then end of a week you would have spent 56,000,000 gold to get 21 diamonds on 10 accounts which is not enough to buy anything. That is without the time spent running all the accounts and moving the gold. It would be far cheaper and easier to use the same amount of gold to buy the items in the Auction House.
The diamond NPC was a great aid to those who had no other way to get diamonds even at a high price and when the rare true sale or special came around you didn't have to rely on player to player trades which far too often were scams. The scammers wanted the diamond NPC gone and got their way.