I would say for CTF the 'main' classes in order of importance are the pathfinder, doombringer, tech and then jugg.
I don't know. I feel it's really difficult to order classes by importance.
A PTH can't do anything if the enemy flag stand isn't cleared. For that you need either JUGs or RDRs. If the enemy stand is cleared and the PTH can get the grab, then it's all for nothing if your own flag gets taken as well. For that you need good flag defense.
Sure, a DMB is an obvious choice, but a DMB alone is often completely useless, if the enemy team does even a little bit of harassing. So this means you need RDRs or other strong dueling classes to take out enemy JUGs in the midfield, you need more mobile defense players like SLDs and even PTHs, who can protect the DMB and return the flag if it gets knocked off the stand.
If despite all your efforts your flag still gets taken, then you need PTHs to chase down the enemy capper.
On top of all this are the Shrikes, which can be used in various very useful roles.
Raider dominates indoors and can harass the flagstand more safely then the jugg. Choosing a raider over the jugg really just depends on the map IMO.
I'd say RDR dominates much more outdoors than it does indoors. When fighting outdoors the only class I'm really afraid of is another RDR (or maybe a JUG who is more skilled than me and is using the X1 and Spinfusor Disks). Indoors tho, anyone with an explosive weapon is scary, since there's less room to avoid their shots.
Also, I feel the JUG can harass the enemy flag stand more safely, since they can shoot from farther away.
I would say play as every role and it will help you understand how you can best help your team. For example only when playing as the heavy on flag did I understand just how frustrating juggs can be. Now that I now I will play midfield soldier more to protect my teams fats before they get too frustrated and switch classes.
Completely agreed. It's very important to try out other classes or at least read about how they are played, what their strengths and weaknesses are, what people who play them are most bothered about, etc. Gives you a much better overall understanding of the game.