The biggest misconception about BFS is that it's the equivalent to ultralight spinning. This is the general mentality of the YouTubers and other social media with a predominately Western audience. Much of that stems from where most of them got started; cheap AliExpress reels and trout rods.
First and foremost, BFS is the reel itself. A light shallow spool, low inertia bearings, and a brake to make them work in unison. Aside from the spool being light weight, the depth also keeps the retrieval rate somewhat consistent. With a deeper spool, the retrieval rate nosedives as you get deeper into the spool. BFS spools, while not immune to this, do mitigate it to some extent. Second, the thinner lines used are also beneficial to casting distance since there will be less friction with the rod eyelets.
Next, the rods. The only rods that come adorned with the BF nomenclature are bass rods and saltwater rods. Trout rods are entirely different, even though the powers and weight ranges may be similar. Bass rods tend to have a more narrow range of weights, mostly because they are para taper which means they bend more in the middle and butt sections. This is required for some bass fishing due to the environments they're found. It's much easier getting a bass out of the slop with a bass rod than it is a trout rod. Conversely, trout and saltwater rods are progressive taper, meaning they bend more in the tip and less the closer to the butt you get. This serves two purposes; to keep the fish pinned during the fight, and offer a wider range of weights to cast. Not all trout rods are meant to cast tiny spoons and spinners, some are meant for larger lures for bigger migratory fish. My three favorite trout rods are 3-18g/4-10lb, 3-12g/3-8lb, and 5-16g/4-10lb respectively. They're meant for big fish and have tapers that help keep them pinned and under control during those runs and head shakes. Those rods were designed from the ground up to work with BFS reels. I use them for lake run brown trout, steelhead, and coho salmon. For those I'm often throwing 4-10g spoons and minnow style baits.
As far as AliExpress trout rods go, most of those are built on American style UL spinning blanks, which are usually para taper buggy whips. They can cast very light lures, but they can't handle more formidable fish very well. For smaller resident trout and panfish, they're just fine. Sure, you can fish bass and larger migratory fish with them, but they aren't the right tool for the job due to their inefficiencies for such fish.