You're mistaken unfortunately my friend. As if you recall, At level 75+, Tank jobs became completely useless in exp parties, Even 6 mans, So while it might help at lower levels, Once you hit 75, You would hit a stone-wall.
If it wasn't for alliance Exp, Most tank jobs, and the ones i named above, Would probably have a very very hard time leveling up. Back when 6 man was king, If you didn't have "Desirable" jobs, You rarely ever found a party. Its sad really. Alliance exp actually helped those jobs get a spot, Since it was less restrictive