Bolts can be anything you want, Cheap and nasty, made with left overs from Chernobyl nuclear plant and meted down in a backyard smelter or Aerospace grade and everything in between.
A cut thread is okay in many applications but not for a cyl head that has a lot going on with thermal-heat issues as well as holding a torque, But a rolled thread is made by FORMING a thread and not cutting one so 2 different processes and the strength is different. But dont get too excited about reports of micro cracking. It all depends on what material the bolt is made out of and heat treating.
Nothing wrong with stainless tho, stainless seems rather misunderstood. No such thing as 1 type of stainless, there is a wide array of common stock stainless (17-4, Inconel and many others) all with specific properties. Norton and Triumph owners have a wide variety of stainless fasteners readily availible on the market and other than some ill advised (IMHO) Stainless axles nobody every seems to have any issues with these other supplys. But most decorative stainless hardware sold over the counter is rather soft material and typically only a grade 2 in strength. In a pinch I culled a large collection of bolts from auto engines in a wrecking yard or 2 and these make excellent donors provided you properly resize them and rethread them.