We're talking about RAW in this thread. RAW, without the optional rule, does not offer any way at all to identify a spell being cast (aside from seeing its effects), and Sage Advice confirms that that's the intent. XGTE gives you an option, which is designed on purpose to preclude the possibility of counterspelling.
I am on record as saying this system is terrible, the optional rule is also bad, and I would never run a game that way. But it is RAW. (I will add that counterspell does need some limitation, it's way too good if you always know what you're countering.)
RAW does indeed not say anything about the process of identifying a spell.
But interpreting that silence to be equal to "you can't identify a spell before its cast" is wrong. If that was the case, the rulebook wouldn't be silent; Sage Advice be damned.
Since RAW
is silent on the issue it is perfectly cromulent to rule
a) "you automatically identify any spell being cast"
b) "you automatically identify any spell being cast as long as you can cast it yourself"
c) "you automatically identify any spell being cast as long as it's on your spell list"
d) "you automatically identify any spell being cast as long as you can see what components are used"
Or indeed
e) "you can't identify a spell being cast - you must counterspell blind"
All and none of these are RAW.
Nobody would argue a group was playing the game badwrongfun if the party Wizard tells the DM "I ready an action to dive for cover if I see the enemy mage start casting Fireball" after all. The rules' silence on this issue is entirely within the paradigm of rulings not rules. The XGE option is an entirely unwelcome intrusion where the designers seemingly forgot this. Luckily it is easily ignored.
Frankly your posts come across as - no way to sugar-coat this - passive-aggressive, as if WotC would reverse a decision by seeing you champion their cause and going over a cliff, so everybody can see how bad it is.
As an alternative, I repeat my suggestion: assume RAW has nothing to say on the issue because it is not meant to be an issue - every spell is automatically identified according to a) above. Or whatever version you do like!
(In reality, it is because "it's not meant to be an issue since every group wants to play it differently")
TL;DR: let's talk about the rulings we find playable and less about the rulings we all agree are FUBAR
