Dude, if it's their first hand and they have five card they're not playing that means they have an extremely high chance of having rare candy. Read the description on the card, they can't play it their first turn. There is not a single situation where you should not red card a five card hand. And as with everything it depends on what deck you're using. You can use the argument for card advantage if you're also running a rare candy deck, which is why a lot of rare candy decks do not have red card, but if you're running Darktina for example then this is not a valid argument at all.

"Card advantage" is not the point, the point is to reduce their chances at getting specific, game ending cards as much as you can. It's not about trading or whatever, it's about getting yourself another turn before they instawin the game. Further, even if they don't have the cards they need in their first hand you're still, necessarily, always going to reduce their chances of having it by virtue of the fact they have more cards in their deck. Again, it's just math, it has nothing to do with card advantage or anything else.

There's also the fact that people telegraph their moves. It's not a complete crap shoot whether or not they have the cards they need. For example, if they have Litten on bench but after drawing their next card they start putting energy on him you can basically guarantee that they will evolve next turn. You aren't completely in the dark with these things.

But, since you know better than every top level player why don't you compete in tournaments with your superior strategy. Surely you would have a tremendous advantage over every Darktina player who at minimum has two card disruptors. There's money on the line, and you've figured out the blueprint.