You are ignoring the big problem. Whatever advantage you think you are getting, your opponent is getting the same.
So you can argue all you want about how awesome the info is, your opponent just got the same amazing info and gets to play with it first.
That is just plain bad.
Jousting by design is meant to counter aggro and be used in control decks.
When you activate a Joust, no matter what card comes out of your deck for the reveal it doesn't matter for the opponent ESPECIALLY if they are playing aggro (unless you are running extreme tech cards like MCT in which case you will be sad if that card gets revealed). It's not like they are trying to guess "oh man this guy played a Joust... I better play around x fast creature". Besides aggro deck these days don't play around late cards anyway so them learning that you have a Ragnaros doesn't matter to them because they are trying to finish the game before that card even comes into play.
Think of it like when Zombie Chow comes into play from a Warlock, they already announced that they are playing a Control/Slow/Anti Aggro deck. Jousting is like that only you get to see a card in your opponent's deck as well.
And this is precisely why that Gadgetan Jouster is slightly better than the rest because it is played as a Zombie Chow which also allows you to scout the opponent. For the later Jousting cards it doesn't really matter much except that they have a higher chance of winning Jousts because you have more than likely played more of your smaller minions already (or have them in hand) so you can make a better educated play (like Holy Wrath in Paladin).
Take the following scenario of my Warlock (playing Handlock) vs another Warlock (they can be playing Zoolock/Handlock):
I play Gadgetan instead of Chow going first in the game. If I had played Chow there I would've already announced that I was playing Handlock so him knowing some card in my deck isn't that relevant anymore. So me playing Gadgetan isn't really that much of a draw back.
However, the card that Gadgetan shows from their deck is relevant because it will let me correctly guess what they are playing and plan out my next moves that way. There's a lot of minion variation in Zoolock vs Handlock.
If I am against Zoolock, I am likely to win the Joust and get a 2/3 which will help me control the board. If it's vs Handlock and say I lose the Joust... I have a 1/2 which is still superior to 2/3 Zombie Chow because the Warlock is just going to tap and then Dark Bomb when he is down 4-6 health so that he has more health to work with in the course of the game because of that heal.
