If Northern Ireland is less exposed to what happens in the private sector generally, and to international trade in particular, then you might expect it to be less exposed to Brexit too. Throw in the absence of a functioning government in 2018-20 and it becomes even harder to tell.

Note that, eyeballing your charts, Northern Ireland has *underperformed* the other nations over the full period you looked at. Its economy isn't doing very well, it's just that that hasn't been affected (much) by Brexit.