Yes, they are in many ways foils. At first glance they appear similar, as if they’re on parallel journeys, but that falls apart once you look deeper.
As an example: Dothraki & Wildlings.
Dænerys brought the Dothraki over to Westeros, yes, but only because she murdered all their leaders, declared herself ruler over the survivors, and told them to fight in a war that didn’t affect them in the slightest, while Jon brought the Wildlings south of the wall to protect them and, later, asked them to fight in a war that affected all of them, because Ramsay would’ve, in his own words, slaughtered every wildling man, woman, and babe living under Jon’s protection.
Dæenerys is ultimately–even when she does good deeds–fueled by a selfish desire for power, while Jon is ultimately–even when he does bad deeds–fueled by a desire to protect the realm and the people in it. This isn’t just clear in their actions, but in their dialogue. Dænerys keeps repeating that she will take what is hers with fire and blood, while Jon keeps repeating that he’s the shield that guards the realms of men.
Dænerys is constantly reminded (and reminds others) that she’s Special (which she absolutely is), while Jon is constantly put through humbling situations where he’s reminded of how privileged he is. Even when he’s back at Winterfell, trying to lament about his upbringing, Melisandre (a former slave) reminds him that he had it better than most. Which means Dænerys is further and further removed from reality to become a godlike creature (one who sits elevated on a throne or on a dragon), while Jon stays grounded (and sits on a chair-like throne directly on the floor, and fights alongside his people).
I think what we’re really seeing here are two different origin stories: the hero and the villain. Only, that’s really simplifying it; it’s not as black and white as that.
“We all have good and evil in us and there are very few pure paragons and there are very few orcs. A villain is a hero of the other side, as someone said once, and I think there’s a great deal of truth to that, and that’s the interesting thing.” - GRRM (source)
GRRM has written morally gray characters, so it is a bit unfair to call Dænerys a villain, because it makes you think of a mustache-twirling baddie who has little reason for doing what they’re doing. I do think her story comes off as a villain origin story, though, where she won’t step into that role fully until s8. Because, so far, we’ve mostly seen her through her own PoV where she views herself as a hero and therefore many of us believe she is one.
Then s7 happened and we got a taste of how she’s viewed by others, like in the Battle of the Goldroad which was filmed from a terrified Lannister army’s PoV. And like when she repeatedly demanded Jon bend the knee, when all he wanted was help in protecting all of them. And in s8, we won’t just get a taste but a full meal. But, because we’ve gotten her PoV for 6-7 seasons, I think that once she does something really awful–something a villain would do–and we do get to see that from the hero’s PoV, we’ll actually understand why she does it. Some of us might even sympathize with it and with her. That’s what I think GRRM is trying to accomplish.
Because we rarely get that, do we? Usually, a villain is just a person who does bad things who our hero needs to defeat. Sometimes we get a motive, sometimes we get glimpses of a tragic backstory, but we rarely get to watch that journey unfold season after season. We rarely get to know the character as someone to empathize with first before we see them do horrible things. But we have with Dænerys.
In her arc, we see what power can do to a person. How easily it corrupts–especially when you’re surrounded by people who worship and adore you and don’t really allow you to be a regular person. We see how easy it is, once you’ve crossed the line and done something questionable, to do it again and again until you stop questioning your own decisions and morals completely. You become desensitized, and Dænerys certainly has.
She starts off as powerless in a horrible situation without any real friends or confidants or means to get the hell out. She has empathy for others, as opposed to being an actual psychopath like Joffrey or Ramsay, and appears to be sweet and inexperienced. She’s a pretty normal person. Only, of course, she’s not. As it turns out, she’s impervious to fire and ends the season with hatching three dragons. Something she managed to do because she, among other things, burned a woman alive to pay life with death.
That’s not the first time she crosses the line to get what she wants, though. As an example, the only reason why Mirri Maz Duur was there at all was because Khal Drogo attacked her people to finance Dænerys’ wish to invade Westeros and take the throne. And once she gives Mirri Maz Duur a cruel death for personal gain, she starts a pattern we see her repeat again and again in the following seasons: burning people alive = profit.
Because, like Cersei, she actively chooses violence–even her good deeds are accomplished with violence–because she benefits from it and it leaves her with more power, stronger armies, and a larger following than she had before. All to invade another country so that she can rule over it, something she in no way has to do but chooses to do.
Jon, on the other hand, is sick and tired of fighting, but knows that he has to keep fighting if he wants to protect the realm, its people, and his family. Jon knows that, sometimes, he has to do terrible things to protect the realm.
He didn’t betray Ygritte or murder Qhorin Halfhand because it benefited him personally. He did it because he believed it necessary in order to protect the realm.
Dænerys burned the Tarlys alive because she believed it necessary in order to gain power and take one step closer to the Iron Throne.
If we really want to simplify it: Jon is a protector. Dænerys is an aggressor. They’re foils–and I believe that’s why GRRM chose to make them the last Targaryens. Not to unite them, but to show two sides of the same coin.
So, I think that in s8 we will see them both do terrible things, but for entirely different reasons. They will murder and deceive and betray. Jon will do it because he wants to protect, because he’ll be the hero. Dænerys will do it because she wants power, because she’ll be the “villain”.
Thanks for the ask, anon!