My character is a soldier and doesn't have a good regenerative shield like the one used by krypton321 in the YouTube video. I am able to get around 50% of the armor down and then both my squad mates die. I had no med gel to start with, so that is another problem. Once the squad mates die, it gets harder to take the barrier down as well. What I have done so far is to run around the platform and then take a few shots.
A good shield would have been helpful. I think the soldier option was not very smart. Without a good shield, collector ship is going to be a problem as well.
Edit: I finished Horizon. Same strategy. Needed to run around the platform. Cannot expect much from the squad. I had Garrus and Mordin as squad mates. Mordin was useful to bring the armor down with incineration as long he was alive. Around 75% armor both of them died. I used rifle and heavy reave until the armor was close to 25% and then used the collector particle beam to take out the rest. Died way too many times. Key is to run from cover to cover and never get caught on the inside. Don't wait for the praetorian to get too close or you will take heavy damage if you don't have a good shield.
Edit 2: On the collector ship now. Completed 4 loyalty missions without any problem (Miranda, Jacob, Mordin and Grunt in that order). The ambush part doesn't look good at all. Died a few times already. May be I will try next weekend.
Edit 3: After 2 hours of trying I gave up on the collector ship as soldier. I also kept seeing the message "Sentinels are nearly indestructible. Tech armor gives additional layer of protection...". So I started a sentinel career on insanity difficulty. So far it has been good. I completed the horizon fairly easily as well because I could restore my shields often. Hopefully that will help on collector ship.
Edit 4: I have completed the collector ship with Miranda and Jack. Grunt kept dying. Tech armor helped a lot.
Edit 5: I have completed the game on insanity. Completing all loyalty missions helped with the upgrades necessary for the final battle. It wasn't hard with all that heavy damages. Took grunt and legion along at collector base because they have shields. Too many harbingers while fighting the reaper though. Used legions combat drones to distract the harbinger. Had armor piercing ammo (tungsten rounds) as the power. Again, thanks to the tech armor.