Okay, let me clear some things. I don’t “hate” training arms, I just don’t enjoy training them, especially biceps. It isn’t that I have inferior strength or development, it’s just because it’s boring.
While most guys would love nothing more than to do 10 sets of bicep curls each workout, I just don’t find direct arm exercises to be all that exciting or effective for that matter.

All you do for biceps is curls. Barbell curl, dumbbell curl, incline bench curl, preacher bench curl, concentration curl, cable curl, hammer curl, reverse curl, seated curl, and the list can go on and on.
Triceps aren’t much more exciting. Traditionally for triceps, you extend the arm—that’s it. But it’s still a lot more enjoyable than training biceps.

PROGRESSION SUCKS ON DIRECT ARM EXERCISES
Most guys start off by curling 5-10 kgs, then within a year they’re up at 20-25 kgs. And after that… progression slows down to a halt.
You’re not going to see many (if any) guys in the gym curling past 30 kgs with strict controlled form. Sure you can find a bunch of guys curling 40-50+ kg dumbbells on YouTube but they are always using shit form or they’re juicing.

The truth is, you won’t be doing 50 kg dumbbell curls with good form no matter how many years of you have been training. The biceps are just too small of a muscle to handle that load.
And this goes for any isolation exercise such as tricep extensions or even lateral raises – you will very quickly hit your upper weight limit very soon and after that increasing the weights you do will be next to impossible.

DIRECT ARM EXERCISES DON’T BUILD GOOD FORMATION
Virtually every major pushing or pulling movement will train your arms. And as you get stronger at them, your arms will grow proportionally in size. Understand that the majority of your arm gains are going to happen by getting really strong at a handful of compound movements, especially chin-ups and dips.
So think of direct arm exercises as icing on the cake.

In my opinion, instead of thinking of arm training as a series of isolated movements, think more whole-body. Visualize your arms as part of a bigger picture of functionality and mechanics, and how different angles, big body movements, and residual stimulation can affect their development.