If you're unlucky enough to get a swing on a target with no Rend. Macros/addons make it a lot easier to track and to use Rend. Why changing target and having the risk of getting a swing on him while he has no Rend and lose the Enhanced Rend thingy?
Edit: No wonder why when you check the top logs, all you see is them spamming Rend but not switching targets.
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Gruul: Your Enrage uptime is good, but your Berserker Rage management is bad. I saw you started your rotation with Charge > Cooldowns > Execute > Stormbolt > Berserker Rage, this is bad in my opinion. If you wanted to use Berserker Rage then you should've done it on the start. I start with Charge > Cooldowns in the middle way before I reach the boss > Bloodthirst > Execute > then whatever. I noticed you didn't have 4p and you also used AM for a 4 minutes fight. You used your Recklessness as soon as it came off cd, which is not good. You should've waited to use Reck on 20% since you wouldn't have an additional Reck on a 4 minutes fight even with AM. Try not to use Glyph of Raging Wind for single target fight. It's always better if you find a glyph that you can actually make some benefit off of it. I saw that you had no petrifying slam on you, such luck.
Oregorger: Too bad you forgot to use Rude Interruption, it's a big factor on your dps. You used your 2nd potion mid fight, which is not good.
In general: You shouldn't be throwing up Berserker Rages, you have to save them for moments you aren't Enraged. The fact that your "melee" is your top damage and it's way ahead your 2nd damage which is Execute (on both fights) is something you need to work on, I think. Most of the times my melee damage is either equal or less than my Execute damage.
If you don't have an addon to track your Enrage, I suggest you to get one. And just practice on managing your cds + Berserker Rages and you will be fine.