"Static" means "fixed". It's a fixed group of people on a fixed set of jobs meeting at a fixed time to do a fixed fight. Everyone learns the fight dance to perfection on one job, so the whole group can clear the fight as efficiently as possible. Statics are generally only really needed when fights are new, and people are still learning the fight.
People only change jobs/roles in statics when the fight demands or allows it. For example, if you can solo tank a fight, the OT can switch to a DPS job. Then perhaps he only has NIN geared, so the usual NIN switches out to MNK. Or if one Savage fight favors DRK but the next favors PLD, a tank may switch. But otherwise, everyone stays on their Main job.
It doesn't sound like you actually want a serious static. You want 7 other people to do fights with you and let you do whatever you want to do. For that, just set up a Party Finder for the fight, and go in on whatever job you want. For Ravana, say that it's a bird/token farming party. Those are still filling up fast; I did one last night on my server.
The idea behind a static is that it is static. Same people, same roles. If you're tackling challenging content, you generally want a specific composition every time, and if folks switch jobs, that's not guaranteed.
Not to mention, the main point behind statics is raiding, in which there is a weekly lockout for gear. Meaning, it takes a while to gear one job, and that takes priority over gearing any other since your contribution to the group on that job is what is vital.
For things like Ravana EX, people aren't often farming them in statics at this point, mostly via PF or DF. I would say either try DF, or have a Party Finder listing, "RavEX clear, eso bonus". Unless you're recruiting at a dead time on your server, and/or you're on a very tiny server, it should probably fill up before too long.
Honestly you sound incredibly Final Fantasy XIV Gil selfish when you put it that way. Static groups are for raiding content, and that content has weekly lock outs. You want to take hear one week from another dps, then tank the next? That's not going to fly.
And for RavEX, you've seen what you can see, sitting back isn't going to help you learn to DPS or Tank it. If that's your attitude a static isn't going to coddle you in to content as different roles while slowing the progression of 7 other people.
However if you think RavEX looks hard or that tank stacking is something you aren't comfortable with them don't even bother with trying to get a Savage Static. The mechanics there might make you wet yourself.