The journal is a terrible way to research fights, really. A vast amount of the mechanics can be dealt with by knowing a few things:
1) Kill adds. I can't think of a fight where, if the boss summons adds, you ignore them. The adds always die. It might only be some of the raid that's tasked with doing this, but the adds die.
2) Interrupt bad things. See the elite adds in Horridon for the best recent example, but in most cases if a mob is casting a spell you want to interrupt it. Again, details might vary - if you're a 10 person raid and short on interrupts you might choose to interrupt Spell A and let B go through, but...
3) Stay/get out of bad things. Fire, axes, void zones... all bad. Move out of them or stay out of them. Do this even at the cost of interrupting a cast because while your performance dips when doing that your performance really sucks when you're dead.
4) Do your role well. This is knowing your class well and having a good handle on its abilities coupled with some knowledge and experience of a fight. Healers should know when to toss out the aoe heal, when to focus on the tanks, etc. DPS should know their priorities and be able to use abilities when they're off CD. Tanks should know how and when to taunt, how to kite, etc. Again, some of this will take practice, but it's not HARD.
Do that and you will be fine in 90% of fights. Yes, there are some fights with odd mechanics but those four points get you most of the way there on the vast majority of fights. Do those and you'll be fine in LFR and probably Flex. In heroic? Yeah ,you need to know more but at that point, you're a heroic raider and kind of cede the right to complain that raiding is hard or complex.