Hmm, I thought disabling an app stopped it until you re-enabled, or at least until the phone was switched off, I don't bother so I wouldn't know I suppose. I am stuck for suggestions then I'm afraid without root.
Rooting probably isn't something you would want to look into being a new user unless Facebook really does cause that big a gripe for you or unless you are interested in tinkering around with your phone that way, and as Mike said, rooting will possibly void warranty and you could end up with a useless brick if something goes wrong.
That said, as long as instructions followed properly and precisely, rooting can be a good thing and reasonably easy when you know what you are doing. You can, as you wish to now, remove bloatware, improve performance/battery life, get custom versions of android and lot's of times, particularly if you are carrier locked, get updates sooner than you would (I am in UK on EE and they are still on Lollipop for G4, probably not going to see Marshmallow update for a while as only last week they pushed another LP update through, my last G4 I had rooted Marshmallow by about November I believe), and there are numerous apps and patches you can have the customise and protect your phone and many other things. That said, it does also make it more vulnerable to attack and just breaking if you aren't careful and there are also some apps that won't work with root (one of my banks block me from using the app with root).
I'm waffling now on something that may not even interest you at all. If Facebook really does cause you that much grief take a look at the threads in the
Android Rooting subforum, probably particularly
General Rooting Discussion - please read BEFORE posting