To me, a class that provides "minor" buffs like that you describe is exactly "splashing everything with glitter." Mages shouldn't dominate plots, but they shouldn't infuse everything either. Magick should be rare, dangerous, and weird, and such a class wouldn't accomplish any of that. It's as much a trivialization of magick as a group of X-Men Gemmed solving all problems are.
To answer the Original Post, the players of magickers get flak because so many of them are (or were) rather blatantly after the coded power that the (sub)Guilds provided. Magick is just codified twinkage. Maybe if it had more coded drawbacks it wouldn't get the same amount of hate, similar to how people rarely disparage mul players compared to dwarf players. Muls have good documentation and strong code limitations, while dwarves only have documentation and no coded disadvantages to enforce it.
I would emphasize a strong WERE for the "blatant coded power" of the mainguilds. But, I would also note (and agree with) an important fact that if you wanted to get anything done as a magicker before, you were forced to use a lot of magick to do it, because magick totally replaced all normal class abilities: combat, defense, crafting, detection, mobility, stealth, etc. Countering your post, there WERE multiple coded disadvantages for mainguilded magickers, namely their utter lack of main-class level abilities that provide basic survival skills and crafting skills. There were and still are the non-coded penalties socially that I think aren't up for debate here.
However, I get you that the "sprinkle pixie dust on everything" is not desirable for Armageddon. I agree completely, it doesn't fit a low-fantasy setting.
I tried to play magickers differently than that. Sure, I would practice a lot with the mainguild magickers in a temple to branch spells, because I wanted to have options; I tried to do it with roleplay, even solo RP, but as much as I could I would involve other magickers in my practice. If I was a rogue mage it would be more interesting then because there was so much more practicing to do (out of necessity) and therefore harder to hide.
If I were going to use mainguild magick I -tried- to avoid using them in too-visible a way. It was challenging at times; the way magick worked would mandate a whole room shaking or something equally ridiculous when you saw the emote. (I still have a problem with the fact that all casting involves chanting, a room-spook emote like a ball of flames or mist flying everywhere). However, things like a few hidden buffs were pretty fun, because people would wonder exactly what the magick was doing for your PC. As such, I tried to avoid say the "stoneskin" spell, or big magickal weapons sticking out of my PC's ass.
As a result, my magickers would often be a little less "accomplished" if coded accomplishment is the point of everything, but they were respected, because I was trying to fit the "low fantasy" theme despite having a broad variety of spells. It also meant that, for example, a drov beetle would randomly 1-hit me BECAUSE i didn't have buffs on at all times that made my character survivable.
(This is in fact how my 30 day+ or whatever it was magicker ended up dying, after having been around for several Arm of the Dragon RPTs and being involved in the stories of other gemmed, some mundanes, some Templars, and some criminal scum).
Conclusion: I do appreciate strongly that the subguilds give magickers some self-reliance without needing to constantly spam magick all day. It better achieves a subtlety of a low-fantasy setting because "getting things done" (i.e., being involved in some plots, staying alive, making contacts) doesn't require twinkly-sparks all day and all night.
I would also add that "choosing magickers for coded advantages" is not true any longer because of some factors that you would understand if you played several of them currently. Overall, I think the GDB hatred of magickers, particularly the subguilds, needs to just vanish as a result of these two things, because it directly deals with the criticisms that respected players such as BadSkeelz listed above. In fact, I would argue these changes went into effect almost fully because of the community's discussions about magickers and these downsides to the old mainguilds that I agree did exist for some players of them.
But, I would also maintain my own counterpoint that at least the way I was playing mainguilds, I tried (and I hope, accomplished) being subtle, I didn't use magick constantly, I kept people guessing; it was possible, but it did require taking a lot of risk (such as by knowing you were unprepared for danger unless covered in magick buffs), it required more patience to await that cool opportunity to have magick play an intriguing role in a storyline, and it required heavy reliance on a subguild that would get you the ability to play a believable Zalanthan instead of just a magickal battery.
I also maintain that there could have been other ways to accomplish subtlety and removing the total reliance on highly-visible magick without just completely removing all the mainguilds, such as changing the magickal emotes, the magickal spell functions, etc.
Note for below: Don't overthink me hailing Badskeelz, just using him as an example of many vocal, active players, players who do often play or have played high ranking leadership roles and who I respect for their understanding of the setting. In fact, I greatly enjoyed playing a particular long lived magicker and interacting with him when he played a particular Lieutenant in The Arm. I would like to think he might not have made his strong opinions if he had more chances to interact with magickers using that shit more like I did and less like the stuff he unfortunately had repeated exposures to.
