I know exactly how you feel, I used to do a hell of a lot with more orchestral stuff (actually marching instrumentation quite a bit), so when I opened FL for the first time I was like, "this is stupid, there's no staff, and it's all loop based... no REAL musician would use this." But as I got more familiar with it, it became much easier to navigate. I still use a lot of high power organic samples in my work (I actually just bought Native Instruments' West African instrument soundpack, and am eagerly awaiting the download at work ). You can import sound libraries by putting whatever you need into the plug-in folder within the FL folder, and then scan for new plug-ins in FL itself.
As for the "loop"/pattern based stuff, you don't need to be constricted to one bar. It sounds like you're talking about the sequencer on the left, which I really only use for percussive stuff and drum programming, and even then, I end up using the piano roll for velocities and stuff. If you right click on the instrument in the sequencer window, you can open the piano roll, in which you can do all your pitch-based work and alter velocities and a bunch of other fun stuff (and go for as many measures as you want). I've heard of people doing all of their work in a single pattern, meaning all the instruments would be in one track in the playlist for the whole piece. I've also heard of people making completely new patterns for literally everything in the song and ending up with about 150 of them. I personally write what I need as I need it, with one instrument per pattern (sometimes more, for chord work and stuff), and then if there's something that repeats, just put the pattern where it belongs in order to repeat properly. There's really a lot of freedom in how you compose, and I wouldn't write FL off just yet
EDIT: And with film composition, there are other DAWs that people use, Nuendo, Cubase, Pro Tools, even Logic and FL have their place in film composition. Really, it's just whatever works best for the composer, whatever their personal taste may be. I personally don't like Logic or Reason, I've used both and they just seem too unintuitive to me, and the automation is nowhere NEAR as precise and easy to use as it is in FL. I've never used Cubase or Nuendo, though I've heard great things about both. Sonor is another one to look into, though again I've never used it personally. If you've ever heard how fucking awesome Vurez's organic instrumentation is, he's a Cubase user, for reference. BGC and zircon both do amazing work in FL. I don't see any reason why you can't do great sequencing in FL or Logic or Reason or WHATEVER if you have the know-how and the sample power. This is the part where I come back to preference. It's all about what you're comfortable using
And hey, to your credit, I just found out that James Horner (composer for Avatar, Titanic, etc.) uses Sibelius to compose and then exports the MIDI to Pro Tools to dick around with. So there's that