Sure, that's fine and dandy but why bother bringing an AST then? A Diurnal AST is basically a White Mage with party augmenting card buffs. If you don't use the buffs, you might as well just erase AST from the game because WHM would become the more logical choice to play. Telling an AST to "not bother using one of their core functions" sounds like a terrible argument.
A player can play optimally as a WHM and SCH without knowing the DPS of my other party members are. A player cannot play optimally as an AST as their performance is directly tied to the performance of their group. Giving your DPS-augmenting cards to those who are achieving high DPS means the AST is giving the most bang for their DPS-augmenting cards.
Those are people you just don't want to associate with at all to be honest. If someone is concerned about "10 seconds" and going to judge people for that, those are people you don't want to party with. A terrible leader will make terrible decisions regardless of they have a parser or not. For all we know said leader was measuring everyone's enmity during the fight (a terrible way to assess someone's skill) and saw that said DPS was under a certain desired threshold. They decided to kick them citing "bad DPS" but they based that decision due to enmity. We don't know without more facts.
So, now the question I have to ask you this. AST's potential is directly based on the DPS their party is out putting. A Balance on a 1,200 DPS will basically grant an increase of 120DPS for the next 30 seconds. Likewise a Balance on a 900 DPS will grant an increase of 90DPS for the next 30 seconds. Using that Balance on the 1,200 DPS is a 33% gain compared to using it on the 900 DPS. So, tell me, how does an AST gauge this decision without knowing exactly what their party is out putting without a parsing tool?
Draw is on a 30 second cooldown. It allows the AST to draw one of six cards that augments a party member(s) between 15 to 30 seconds. There are ways to make this buff longer, extend it to other party members, and make it more potent. Usually you have to decide who to give the buff to depending on the fight parameters and party resources / damage.
Funny enough, it's probably better giving single target Arrow / Balance to the better DPS in 4-mans versus AoEing it - especially if you have a very good NNIN or MNK and you get Enhanced Arrow. That's an incredible attack speed boost.
Likewise, it's not always possible to Royal Road an Expand and ASTs should never be trying to hold cards for "the ultimate draw". Like most cards in the AST kit, it's all a matter of circumstances and deciding which decision is best for their party and holding cards / Royal Roads to achieve a specific effect is very limiting to the AST card kit.
As Ragology pointed out earlier:
Arrow increases your Attack Speed. This is similar to how Greased Lightning and Huton work and stacking Attack Speed effects with more Attack Speeds effects has incredible returns. Also note that Attack Speed is different from SkS and SpS because it doesn't affect your HoT/DoT potencies and Attack Speeds affects the GCD of both of your weaponskills / spells and your auto attacks (I believe SkS only affects your weaponskills).
Spear reduces the recast time of your abilities with cooldowns. The downside to this is that the player must have Spear on them when they activate their cooldown or else they won't get the reduction (sadly Spear isn't retroactive).
This can be a DPS increase for some Jobs like NIN (faster Ninjutsu), DRG (more Jumps / Leg Sweeps), and MCH (oGCDs oGCDs oGCDs!) since they have oGCD abilities that are generally on short cooldown. In the case of Jump, you're reducing Jump's recast from 30s to 24s if they use Jump with Spear up.
As Kabzy pointed out earlier, this comment completely misses the context of my opening post.
AST's performance is directly tied into the performance of the party they are with. Without a way to gauge the party members accurately, the AST will find it difficult to give their DPS-augmenting cards to the correct players.