Yes, colonialism was not profitable. They did it because we hadn't invented modernity yet so we didn't know how to be profitable.
One reason "Britain" (the UK) exists is that Scotland tried to get into colonialism, bankrupted themselves, and had to sell themselves to England.
Generally speaking, getting a lot of resources is actually bad for your economy because it outstrips your ability to develop value-added businesses and institutions: https://en.wikipedia.org/wiki/Resource_curse
> Compare a per capita GDP ranking of European countries:
You're arguing with a Maoist (or someone who's been listening to them.) One thing about these people is that they believe Finland and Ireland are colonizers, because they just think all European countries are the same.
FWIW, Mao had some good ideas, and some crazy ones. Like most historical figures, really, but even then I wouldn't take being called a Maoist an insult. That said, no proper leftist of any stripe would call Ireland a colonizer nation. They may have attempted it, but the subsequent ratfucking on the part of Great Britain ever since then and their continued existence inside the geopolitical abusive relationship that is the United Kingdom brings them far closer, ethically, to the Congo than to Britain. Lest we forget fun times like the Great Famine, or as the Irish call it, "that time Britain took all the fucking food." Or, more accurately the landlords did, the handling of which is one of Mao's better ideas.
It's a rich nation with a welfare state and universal healthcare.
This is an issue for anyone whose philosophy says that all rich countries got that way by stealing their wealth from the third world.