You have decided to get into the semantics of conquest vs land theft. My reading of your reply is that conquest is an excusable activity?
My understanding of your argument rests on that everyone does it (conquest) so what the British Empire did was only unique in its scale.
I think your question and argument takes on more a personal morality question and I will present you with the way I think about it.
A couple of questions, if you have different answers to me then we just have different personal belief systems and we can leave it at that.
Do you excuse murder, rape, kidnapping, robbery in your current life as just being something people and chimpanzees do?
If the answer is no (I am sure it is) then why do you say conquest is excusable? Which by my definition is just larger groups of people engaging in the above mentioned crimes?
I do not want to be celebrating an organisation which is responsible for those crimes.
Finally, indigenous people's violence (and remembering there are 1000s of nations across the world which is kind of ridiculous to be saying them all at once) does not culturally define them in the same way mass violence defined the British Empire.
Violence, oppression and misery was the modus operandi of the British Empire.