I think it'd be subverting expectations. From the start you might think it's about the Pacific trash island that has collected there, but then it turns the other way and calls Puerto Rico a trash island. A decently funny joke imo, even if rude. I've seen the same joke being done about the UK and it did get a proper chuckle out of me.
The main difference is that the UK used to be powerful and did a lot of bad things to a lot of countries around the world. Puerto Rico on the other hand has always been weak so it feels weird for someone in a much more powerful area of the world to pick on them.
Jeselnik is a class act. What's interesting to me is that the guy in the op, essentially has the same Roast style as Jeselnik. But the way they execute it is key.
I saw some of the ops bits from a comedy central roast, and they were really funny... But when you put him in the context of being at a trump rally wave saying stuff like this it's like "ohhh, you're not making subvertive jokes, you're just a bigot hiding behind 'comedy'"
It can be meaner but for a stand-up I think it could be fine, if the context is comedy and it didn't have genuine hatred behind it. In this case it's clear that it was used as a tool of hatred and not just for making a joke.
I don't think how places used to be plays any part in how funny insulting them is. Despite being as powerful as the UK when it was last relevant and worse, I think people would still be offended if he said Japan instead. "Always OK to hate colonizers" as someone put it my butt, the internet just really wants to make fun of France and not feel bad about it.
If by recent past you mean the genocides in their most recent wars with their neighbors then yes, I would say that would qualify them to be made fun of in that way. If you just mean some industrial successes in the 1980s, not so much.
I don't understand the joke because everybody knows the trash island (not an island btw, you cannot walk on it) is in the Pacific Ocean, and Puerto Rico is on the Atlantic Ocean, so it's inaccurate. I mean... geography is important, otherwise, you could do the joke with any island in the world and as a French, I would of course pick Great Britain.