Ghost was mostly just chilling for Jon’s last few battles, man. And I’m certainly okay with Jon topping the list. Now for the rest of it, I’m hardly an expert on medieval combat nor Game of Thrones, but judging from what I’ve seen in the show, I think Grey Worm is probably pretty fairly ranked. Remember, he’s a soldier, not a knight, whose primary weapons are a shield and spear. They’re meant to work together as a phalanx to defend and overwhelm the enemy. You saw how the Unsullied fared in less structured battles, like the gritty urban combat of Mereen. They’re not typically highly skilled on their own, but they work as a unit. Grey Worm is likely the most talented of them, but he falls behind guys like Daario and Jon Snow, probably. Again, I’m just going on what I’ve seen and intuition — I’m no authority here.
Although, he and Tormund would be an interesting comparison. Tormund seems to have an overwhelming style, someone who fights with power and raw emotion, less of a skilled fighter. That might be enough sometimes, but I think in a one-on-one situation, you’re probably right that Grey Worm would take him out, having his training and skill to rely on (as long as Tormund can’t Hound/Mountain style just straight up overpower him; Grey Worm seems like quite the slight fellow, but lean muscle is in these days).
I don’t remember seeing Loras fight well enough to place him, so I can’t say anything about him. Brienne is a total badass, though. She took out the Hound, she fought a bear; almost hard to say she isn’t the best. Glad she and Jon are on the same side, I’d hate to see them have to fight each other.