Just got to reading this, my bad.
No one playing any class should full rely on Simple Mode, that's not its purpose. It simply does the tedious, repetitive rotations for people, but everyone still has to use other important skills alongside Simple Mode. So you're correct on Gunner, 4 > V > Tab > Simple Mode. With your ms you should be able to sometimes cast 7 Bullet Storms, which would show 35 hits in the parse, each one hits 5x.
As Fire FM, Simple Mode doesn't prioritize using Dual Dragon before Inferno, so Inferno does not get the extra 15 second reduction needed to completely reset the cd.
My Simple Mode is binded to RMB for me, so for me the correct way to start off would be something like LMB>RMB>2>LMB>2>1>4>X>Hold down RMB(Simple mode).
The second LMB+2 gets me 5 Ember Stacks, so I can use Shock Fire for the Inferno insta-cast, then Simple Mode starts off with Dual Dragon(lowering Inferno's CD by 15 seconds), the additional Inferno cast and Blazing Wall(which also lowers Inferno CD by 15 seconds as well as resetting Dual Dragon), then it'll use Dual Dragon again, which lowers Inferno CD again allowing me to immediately cast it 2 more times. This maximizes your burst and it's how you're supposed to start every time you get a weapon reset. You want to get 1>4>X off before using Dual Dragon all the time. It can feel awkward and clunky, but get comfortable with it and you'll notice an improvement. The purpose of me using 4 in between is because often if you just try to use 1>X, the Inferno won't be instant, you have to give it a slight delay for the Shock Fire buff to actually work, but I prefer using 4 in between instead.
For gunner, your opener is the same as mine, except I start with a stun for Hae Mujin, so 2>4>V>Tab, then I just hold down simple mode, during my 2nd Bullet Storm, I start spamming X and immediately after, continue holding down Simple Mode. If I'm fast enough, I can still get the 7th Bullet Storm before Tombstone is off, then immediately use my C, and continue on with Simple Mode. For gunner, you should almost never release the simple mode button. I try to line up my CDs, I don't like to use C if I don't have my badge up, so if the V is almost off CD, or I have a reset coming, I'll sometimes wait for Carpet Bomb before using Firefall.