I'm not sure why Dua Lipa being an interval act would be an affront to her country? Like no time commitment to BBC, would likely be compensated much more as an interval than by a broadcaster, no pressure of competition, a higher degree of promo (10+ minutes rather than 3, plus headlining). I think just about anyone stands to benefit much more from having the luxury of being an interval than representing the country.
Anyways, I'm pretty indifferent to whether there's a big artist or not. I don't see much harm in it though