I'm aware of that, but as someone who played Gauntlet, which is even more different than constructed, a lot (I'm getting close to 1000 wins), I'd say that if we were to measure how minion quality matters, Rift would be between Gauntlet and constructed, leaning towards constructed due to rerolls. Why? Simply, in Rift you have a solid basis that you can turn into a crazy deck step by step, in Gauntlet you needed more or less RNG to get an incredibly good deck, depending on the faction. In Rift rerolls allow to skip the RNG almost completely if you have a lot of dust, which makes it less of a great mode for new players and Duelyst desperately needs a newbie-friendly mode, IMO. Hence I'd like to see the reroll option removed to make it more fair for everyone.
Again - you have starter decks only at the start. The further you go, the crazier they become. Fountain of Youth was even one of the worst picks in Gauntlet, beaten by almost all Rare cards (and exceptions were as good as Sol), so if you picked that for some reason, it'd likely be your next replace - basically a wasted "upgrade". Even in Sajj starter deck (not the best one for sure) I picked I saw no card that's worse - golems are much more solid, Blindscorches are more reliable with BBS, Necroseers aren't worse either and a single Putrid had already been replaced with removal. The rest of the deck - much better. I'm wondering what you'd replace into that card.
In contrary to Fountain it's not one of the worst cards in the game, I can agree. However, imagine someone picked an Aymara in its spot. Then Storm Kage vs Revenant. A similar thing happened let's say 10 times and you encounter that deck on level 20 (assuming you were able to reach it in the first place with this deck quality). The person got that high so they're not terrible, do you think that on average you stand a chance with a deck consisting in 25% of memes against a deck that has one of the highest quality minions in their place?
As for removal, it's much more likely than in Gauntlet since many starter decks have 3x of staple removal cards in the first place.
Or at least show 6 generals so that it's 50% to get what you want like it was in Gauntlet.