Sigh.
arbitrary
–adjective
1. subject to individual will or judgment without restriction; contingent solely upon one's discretion: an arbitrary decision.
2. decided by a judge or arbiter rather than by a law or statute.
3. having unlimited power; uncontrolled or unrestricted by law; despotic; tyrannical: an arbitrary government.
The use in question is #1. No "impulsive or irrational" anywhere near there.
The levelling system is this:
1-a) Get xp.
1-b) XP can be lost if you die.
2-a) Level up when a certain amount of xp is obtained and your level is below your level cap.
2-b) Do not level up if your current level is equal to your level cap.
Any restrictions you choose to place on it are arbitrary restrictions, and cannot be used to define cheating as you are doing.
There is nothing stating how you HAVE to gain the xp. Scrolls have been in the game since the US release (I have no idea if eco warrior was there at the JP release). The purpose of these scrolls is that they provide valuable insight on the world, combat, politics, whatever that your character learns when reading them. They have a job level requirement to ensure that your character is experienced enough to understand the insights on the scroll.
If SE wanted you to be forced to use Dominion Op xp on the job that "did the work", they could have done so. The precedent is there with campaign ops; once you meet the objective, you get the xp, and AN are given on reporting back.
While Campaign Ops are mentioned, many, like Vanguard-X, Crimson Domino, Bridge Too Far, Street Sweeper, Steel Resolve, Magna Cache, Crystal Fist, Iron Anvil, Hawkeye, Slaughterhouse, Prying Eyes, and Cut And Cauterize do not have any combat involved. Crimson Domino sometimes even expressly forbids you to fight anything, while giving you a direct path with no aggro in some zones. Taking part in these is not cheating the leveling system.
Stock and Awe and Materiel Storm can have combat if you farm the requested items, but the NPC says he doesn't care if you farm them or buy them off others, just bring them to him. The point is to have the items available for crafting for the war effort, not how you get them. For those two ops, its always items that can be bought on the AH, usually crafting materials.
Hazardous Materials gives you a Silence, Amnesia, and Gravity effect, so it is more about avoiding combat. Bailey Borer can be done only attacking the Fortilace, while being out of aggro range of anything that will fight back.
Offensive ops, defensive ops, Frozen flame, Deep Cover, Brave Dawn, and Delta Strike are the only ones that definitely involve combat.
Keymasters are contributing; It boosts the time remaining, lights, xp, cruor, temp items, lootpool items, and key item supply of the alliance. You can't claim that buying keys using cruor obtained on another jobs is dishonest, because cruor is the gil of abyssea. It is their money, which is tied to the character, not the job. To claim otherwise is equivalent to claiming that gil earned should only be spendable on the job which earned it.
Xp per kill scales to level, dominion ops scale to level (below 75), and boxes do not scale. If you think the way you can get xp in abyssea is not working as intended, file a bug report
here (link).
On the issue of uncapped primes avatar fights vs 20 cap prime avatar fights:
In ye olde days, there were no lv 20 cap fights. The only way to flag the fights was to nearly cap fame in the zone (instead of lv 2 or 3, whatever it is for the mini fights). Back in those days, the avatar fights were considered hard; wipes with a full party of 75 were not that uncommon. Summoners complained that it was too hard to get their summons that way, especially if they were trying to level smn as their first main job--they were not high enough level to do the fights, did not have the gil to buy a spot, and were considered gimps with only carbuncle and spirits. To solve this, the mini fights were added, which allowed summoners to do a solo version of the fight at lv 20, with the sole reward being the ability to form a pact with the avatar. I happened to have all 6 prime avatars before the mini-fights were available; that does not mean that I took the easy way out or cheated. You don't "learn a spell" when getting a new summon, you make an agreement with the being to be summoned. The ability to call the agreement into effect requires the summoner job. Spirit pacts are slightly different in that you use a scroll rather than meet with the being in question. As such, they scrolls can only be used by summoners.