It's the GM's game man, it's their job to do whatever they need to tell the story they wanna tell.
Yea, see this should never be the case, the GM's job is to create a setting in which the players can create a story. If you run a game as it the GMs story, deal with it I bet you change players often because that is railroading and players are not fond of that. Players are there to have fun and play their character and build their character's story, that is the point of any RPG game regardless of the setting.
As to drain forget it, the dragon won't take any at force 20+, reagents are cheap. Dragon's scale better and have greater base values and basically unlimited resource, I care nothing about armor it's easier to make sure the characters miss, and there lots of way to do that. Combat sense is just the most simple and efficient method.
I try to forget the FA reagent rules because those are stupid and make reagents way to powerful, plus would a dragon really be willing to destroy some of its own scales to cast a spell, much less use reagents? Remeber, dragons find reagents distasteful to use. Either way, making a character always miss always upsets players because eventually, they will just say fuck it was dead and leave the game. A thing we as GMs should be trying to avoid, especially as good players are a rare find.
Dragon can have whatever resources the GM feels is appropriate, pushing a 24 casting pool to 36 in single spell category is very easy to do at that level. As a GM you should know it's not hard, if you want the result to be 12 then take the steps to make it 12 or 14 or 18 it's not a mathematical challenge, pick the average you want and get the pool 3 times result; Problem solved.
You are right, they can have any stats you want if you just up their magic rating when it comes to spellcasting. However, making something a challenge instead of a "welp the dragon/baddy is here, we are all now dead" without a chance of survival is more around the math, because multiplying the successes isn't always the best way to go since you may base the successes you need off of the average you have seen a player roll in terms of successes and those all just happen to be really good rolls and not the statistical average.
It's also worth noting any time a team has trigger the summon dragon condition the party has epicly screwed the pooch, so kids gloves are off the team gets whats coming to'em TPK or otherwise.
If this was the case, then adventures that are written for your average runner (not prime runner) would not have a dragon coming after them as something that could happen on two of the four possible options. Especially while also having it be possible to get away from the dragon, so having it where the gloves are either on or off is bad GMing. The gloves should never be on in the first place, it should always be a challenge, but one where it is the player's story and you as the GM just fill in the pieces.
But there's no shortage of more intrusive and destructive methods to reach the same result. Come on now I've been gaming for decades man, I've seen all the tricks.
I am guessing you are referring to killing a dragon with this, but why would you want something more pink? The idea would be to end it quickly and disappear not leave even more evidence than you already are that you were there.