From what I can tell booking through Iberia does give you premium lounge access in Doha as well as lounge access in embarkation points . I don’t think IB fares book into p class like QR lite fares to.
sub question what route are you flying , as I know sometimes IB try and change flights once booked to use their own metal or re-route you once the booking has been made . You also have to deal I think with IB customer service as it’s their ticketing rather than QR if there is any issues . Thinking of booking some tickets next year but am a bit nervous going through rather than booking direct with QR , even though fares are cheaper via IB - thanks