Fanaelialae
Legend
Sure it can be a thing IRL. But having one person burning a reaction to make a difficult Arcana check (DC 15+spell level) and shout out info to another who then might cast Counterspell seems inorganic to the game. Why can't a trained caster with sufficient Arcana (the study of spells and spell casting) make this observation and react to it? People make Passive Perception checks to detect invisible foes to a given 5' square all the time (don't get me started on that...) in this game, after all.
Like I said, I prefer them combined as well.
However, keep in mind that making a non-passive perception check requires an action. You don't make a passive perception check; it's just the DC your opponent uses to see whether they are able to hide from you.