This is where I’m see’ing your main issue, your trying to PvE the FM, the only reason we PvE summoners is because there are 2 targets, And he can use 1 to get in the way of the other as well as attacking you for free. The FM can not emulate this. Your rushing your attacks and not using the full timer of your stealth. If and when you get in stealth against a destroyer FM or BD you need to 1. Backaway 2. Stop moving to hope they lose sight of you, then creep in this is where your 3 (which is ranged) can be used to stealth reset as well as stun giving you a free approach from any direction.
I always keep at least 1 point in time bomb so often Ill run at him place the bomb run through him, proc a sneak attack with shuriken Blade And Soul Gold, then I’m good to go, I don’t even need to hit him again from stealth.
5. Again, Utilize COUNTER, BACKSTEP (Breaks ICE) And also smoke screen. Typically you will get frozen during your offense, now you backstep and continue your assault. If your built to Combo spec and not PvE with all your options you can continue your stun and do dmg instead of being left trying to get back in stealth before you die.
Keep in mind that the non healing version of smoke screen has a much shorter cool down.
6. My main ‘Openers’ are BNS Gold. Counter 2. Tab switch (even without infiltrate follow up.) If its not there just moth him and walks towards him hoping it pops up, if it doesn’t Counter in to stealth or back step away to re-engage. And SNEAK ATTACK.
Sneak attack is our best move, hands down. You need to have it available as much as possible. This leads me in to my final bit of advice.