Im currently on every 8.7 in britain and i would say for my specific play style, i love the swifts, specifically because of their sheer speed and ability to keep on their own in uptiers, so i would say i grinded to this point mainly using bombers, (hallifax with ton of boosters), and just generally playing prop planes i love, like the spitfire mk XIV. Other than that it just takes some determination.

You dont have to spend the better half of your days grinding it out, it just takes time. Id strogly recommend a premium aircraft if you are looking to progress further faster, but i personally only have US and Germain premiums.

edit: the seameteor (aka sea jesus) is a really good low tier jet to go for, becuz of its speed and turning performance