^^ looks hard man!
i used to have the same exact problem you have
i found that you just need to annhialte them
i start my shoulder routine with heavy presses and then i would hit either front laterals or skip those and go right to side laterals.
first i would do 3 sets of seated dumbbell side laterals with perfect form of 20, 15, and 12.
and then i would do standing giant sets. i'd start with a 30lbsx8, then 25lbsx8, 20lbs, and 15lbsx8 all consecutive with no rest.
then, allow a 2 minute rest peroid and repeat.
the agony you will feel will be almost unbearable but you have to push through. and this isn't the only way to do a giant set but it's how i like to do it.
after all this, i would go do 3 sets of cable side laterals behind the back. it lets the delt stretch better and reduces the cheating possiblilty.
on these giant sets, don't bent your arms so much. just a little. make it hard for your delts. it looks rediculous when people bend their arms 90 degrees and swing their back and the weights up. that doesn't do a thing.
i would do this particular routien for the side deltoid every third week to prevent overtraining.
i had this problem for a while and they just blew up.
after you do this, you'll get the idea of just how you have to train your deltoids and then you can try getting that same pump/exhaustion/fatigue via other means.
other ways i use to beat up my side delts
seated side laterals supersetted with wide grip upright rows
high rep sets like 20 reps with the heaviest weight possible making sure you still have good form.
alternate arms for side lats either wtih dumbbells or cables but never put the dumbbell/cable down. go from one arm to the other non-stop for a few sets.
hope this helps.