Just reached Crystal rank, here's my tier list

SS: WHM
S: SAM, NIN, DRG, RDM
A: SMN, BRD, MCH, WAR, AST, SGE, SCH
B: MNK, DRK, RPR, PLD, BLM
C: DNC, GNB

The reason I rate WAR only in A tier is because yes, it's great when you have team following up, but this is solo queue so you have to expect every one on your team is bad and the enemy team is less bad than your team, so you're going to have a much harder time solo climbing based off WAR's individual impact alone than you are with the higher tier picks.

The individual impact of a WHM or the other DPS mentioned ahead of WAR will give you far more victories on average than a WAR, since WAR will leave you initiating only to die as your team chases (and dies to) some random SAM/NIN/DRG in your spawn while you're guarding against 4 enemies on the point. Or you attempt to peel, only to lack the damage to secure any kills, because your team mates aren't as good as you so they only do 140k damage while you're at 800k. You're very unlikely going to reach 1 million damage on WAR, something that's almost necessary to climb to crystal rank.

For awhile, I thought RDM was the best DPS because of how easy it was to play and how good it could be at singling out kills. But as I climbed further through plat and diamond, I realized that's where RDM is weakest. It's a duel job. You lack a lot of team fight potential since the only reason you should ideally be in White Shift is for the silence on your Resolution. SAM is the best DPS to play for climbing because they also excel at dueling while also providing better CC, mobility, can spawn camp and their potential to multi-KO. The multi-KO is very important and will very often win you many, many games. I also put DRG above RDM for this exact reason: they're mobile, far tankier, can do similar damage/burst and have multi-KO potential. Multi-KOs win games.

But NIN I think is slightly better than DRG and slightly worse than SAM because of it's ability to disrupt "standard" play. NIN can very quickly and easily single out enemies as they're respawning and escape, causing multiple people to chase them fruitlessly, and just overall break up the "spawn, rush to point, fight or die, repeat" pattern. This causes more "staggered deaths" to happen, where your team is 4 on the point while the enemy rushes one at a time per respawn only to die, and repeat until they lose. They're supposed to wait in spawn invincibility for their team to all respawn together then rush as a group, but no one does that no matter how much you spam "Fall back and regroup!" so a NIN will pick off those stragglers and give the rest of their team a far easier time pushing the point. They're also deceptively tanky. SAM can do a lot of this too, but NIN is slightly better for mobility and time-to-kill potential.