I have to wonder, if Sauron was successful in conquering Middle-Earth, that would mean that the Uruks wouldn't be in an extreme situation. So, if they were behaving that way due to their extreme situation, would they continue to behave the same, or differently?
Orcs are naturally evil in Arda. They're twisted forms of actual beings to suit Morgoth's desire for power. Conquering all of Middle Earth would not change their nature and their very existence is an affront to the Valar.
In regards to the Orcs/Uruk debate: These are not Uruk-hai like Saruman's at all. The game uses Uruk to refer to literally every orc, and it's ridiculous to believe that every orc in Mordor at this time was an Uruk-Hai. There's even that one character you first raise to warchief who is a scrawny little goblin. There's nothing wrong with using Orc instead of Uruk, the game developers mostly did it for style/uniqueness, every other game involves killing orcs but Uruks are uniquely tolkien.