I don't think you should be too hard on yourself for feeling this battle was tough. There's a lot to learn, and you'll start to absorb it as you go -- for instance, you'll probably have a hard time forgetting that normal-types are weak to fighting-type moves, thanks to this victory.
Unfortunately, it's a major flaw in the series that there's certain vital information that the games just don't give you. Type match-ups are so fundamental to Pokemon that I don't think there's an excuse for not having that data easily accessible to the player in-game.
Similarly, move data isn't as accessible as it should be, and your post provides the perfect example of that. Off the top of my head, I don't think you've caught a Pokemon with Retaliate before, so in the context of the game, there's no reason for you to know what it does. Retaliate does double damage if it's used right after a team member faints -- your poor Blitzle probably didn't stand a chance. It's also a normal-type move. With all the data available, you probably would have chosen differently -- if you anticipated Retaliate, you might have sent in the rock-type Roggenrola, which would take half damage from Retaliate. You definitely would not have risked keeping in Throh without healing him. You might have switched in Timburr and hoped he lasted long enough to get in at least one super-effective attack before bringing Throh back out.
So while I don't recommend just playing the game by just following a FAQ or something, I also feel that the game is greatly improved by having easy access to type and move data. I've linked a few pages before -- somewhat reluctantly, since I know from the movie podcast that you're spoiler-averse -- but I think access to more information, such as what Retaliate does, at Bulbapedia (http://bulbapedia.bulbagarden....) might help you begin to put the pieces together a bit more.
Normally, I would never consider strategy guides, but my fiance convinced me that Pokemon worked better with one. Considering the number of undocumented game features there are, I have to admit that getting the pokedex at least has made the game more enjoyable for me.
I wouldn't say get a strategy guide, but in White there's a rule with Gym leaders. Their strongest Pokemon is always 4 levels higher than the previous one. So if Lenora's Herdier was lv21, the next gym you need to be ready for level 25. As for tweaking strategies in gyms, that's what the trainers throughout the gym are for.
When it comes to other human, unpredictable trainers you just have to cover as many bases as you can and hope things fall the way you want.
Also Normal type Pokemon are horrible to fight against due to stupidly high attack and defense, so Lenora's pretty tough considering she's only the 2nd leader. My Stoutland routinely wrecks people's s***.