Well, a conquerer is still a conquerer.
It’s like “oh, he was a NICE slave master.”
Sure. I think we can agree that this was the way the (ancient) world worked without exception. They all conquered or were conquered at some point. I think it’s thus fair to look at what set the respective conquerors apart. Just giving a bit of biblical perspective on the matter, instead of the usual Greek Persian-bashing. ;o)
I think Cyrus should be considered a special case as a truly enlightened ruler. His tax rates were lower than what even the poor in the US have to suffer, and slavery was actively forbidden in any land under his control. He even paid fair market value for land appropriated for his projects and allowed for greater freedom of religion than just about any government before or since.
The Bible doesn't generally make a habit of praising foreign rulers; that it did so for Cyrus suggests that he really was as depicted.