Apologies for not replying with quote, I'm being a little lazy. Also, for the record, when I say "Toxikon" I really just mean whichever version you're used based on content, so sorry if that made anything confusing. At level 90, this means Toxikon II.

The issue with needing E. Diagnosis to break for Addersting really only exists for your opener when needing 2 of them to use both Toxikon and SGE Continuation. You can very easily get Addersting very quickly by putting E. Diagnosis on the main tank prepull since autos in any fights where a perfect opener matters have bosses that auto hard enough to pop the barrier quickly, in which case using one alternative source for your opener does exist. It also pops very quickly everywhere else, even in dungeons, when placed on the main tank. Once you get passed that point, the idea is that you'll prepare your Addersting ahead of time using E. Diagnosis rather than only using it as the cooldown is coming off. How much you'll prep your Addersting will depend largely on the fight. P3S, for example, has a few movement-heavy phases where you will want to have an empty tank to afford the E. Diagnosis uses that will work in favor of your mobility. Beyond your SGE Continuation, though, you really don't need to use Toxikon on cooldown outside of burst windows since it's net neutral. The only time where it becomes a problem is if you end the fight before spending all your Addersting because it means the uses of E. Diagnosis or other gainers ultimately did result in a loss. I'm sure there could be anecdotes about someone who hit enrage at 0.1% where that could've been avoided through more apt use of Toxikon, but that would be an incredibly rare occurrence, and if you cleared the fight, then you still cleared the fight.

That stays true for other GCD gainers as well since it's DPS neutral. So long as you're able to generate some of your Addersting from E. Diagnosis, which isn't hard to do when you don't have the pressure to do it constantly, then you don't need to use those gainers on cooldown. You only are pressured to if you've neglected to gain a single Addersting from E. Diagnosis use once per SGE Continuation timer. Even if that ended up being 60 seconds, is it really that much to ask that someone use E. Diagnosis once a minute or less based on coincidental generation used from your other sources?

This would actually make how many Addersting you're holding onto and what's ideal for any given point in a fight very fluid, which would be very unique to any job in FFXIV, and not a bad thing either. And because it's all net neutral for Toxikon, someone who chooses not to generate or use it throughout a fight outside of maybe getting it through your other methods like Physis II is only really going to lose a small amount of DPS exclusively from ignoring burst windows which is something people already do all the time, even in Savage. The only real demand to use it stems from the SGE continuation concept. Toxikon is more about offering skilled players a way to express mastery without actually performing that much higher than someone who isn't, but you'd be a more effective healer for doing so.

And sure, the healing requirements of FFXIV are rock bottom, but making situational use of E. Diagnosis a good strategy rather than an objectively terrible one 99% of the time is something I'd argue works well in favor of giving SGE more to do with their GCD--something that is very largely a choice.