First, don’t cancel his 3rd skill, the defense down applies at the end of the skill. You need to stack the buff on his T3 skills with the one on his 3rd skill. Proc on the T3 skill then 3, then 2c4c5 (proc now on 5. That should take like 3-5 bars depending on your build. The problem is that if Corvus iFrames you loose the rotation and the buffs. Your best bet is SW mind control so you can do all that perfectly timed.
Don’t believe you can cancel 3. This skill also has the all DEF down but he doesn’t throw his grenades into the end of the animation. It’s also when he is out of iframe and the most vulnerable. You need the all DEF down from 3 to stack with his T3 skill.
It’s more of an art then a science.... I also have Cap & Wanda in as strikers (both of whom have all DEF down skills). So close as I can tell, the key is getting these (DP’s) two skills to stack as much as possible, then unleashing 4 & 5 as both will get you that huge burst through the health bars. I use 1c2c 3 5c4. More or less to fill up the T3 skill as much as possible. 1c2c Coop Skill (RNG). Then the T3 skill will be close to charged. I try to use the 3 skill (with full animation) on the front and back sides of the T3 skill, then 4 or 5 for the burst. Currently ranked Top 50 in PM WBU so hopefully this helps and makes some sense.... Good luck.