For me, I have more experience with Slime and its vast moveset potential. I only was able to really play DQ 1, 2, and two of DQ Monster games. None of the Heroes stand out to me as much as Slime does to me. I never had an issue with the whole "bleh, generic character" when it came to Slime. At one point, I had that mindset, but then I realized that I can't really say that and be fine with any Pokemon(who are all generic monsters in the exact same way). Never mind that Slime is equivalent to Pikachu when it comes to being a mascot and a full character depending the game. Literally the same role as Pikachu in the anime at times too(being a major character, partner of the more generic playable hero).
Besides that, they aren't as well known as the general Pokemon Trainer class, which is what was chosen for Brawl, but even he(and now she if you choose) isn't directly playable. The Pokemon are. Dragon Quest has always had a serious focus on how important the Monsters are to the series. The Heroes/Classes still play their respective role, of course, but people know Dragon Quest because of more than who you play as(and in many cases, not many remember who they are. Some barely know who Erdrick is since he wasn't even playable in the first game alone, just mentioned. He's not that easy to remember compared to the mascot of the series).
I respect your opinion, but I have to disagree with it. Heavily.
The monsters are a part of the series' charm, but they're not as important as the characters, worlds, and stories. That's what makes DQ games memorable, not necessarily the monsters you face along the way. I can understand none of the heroes standing out to you if you've never played any of the main series games past 1 and 2, but I can assure you that they're far more important, and representative of the series as a whole than the random Slimes you defeat on your way through each game.
I've never played any of the DQ Monsters games, nor Rocket Slime, or anything like that, but I
have played quite a few of the main series games and hold them as some of my favorite JRPGs ever. I don't want to sound rude, but in the main series, Slime isn't really anything other than an enemy encounter. They, along with the rest of the monsters, are just enemies you defeat on your grand adventures. Representing all of the main DQ games with Slime would be a huge misrepresentation of the series, in my opinion. The heroes might not be as recognizable as Slime to those who don't really know or care that much about the main series games, but the heroes represent their series as a whole far better than a Slime ever could. Mascot or not.
Basically, Dragon Quest isn't about Slime. It isn't just about monsters either. Dragon Quest is about the stories and adventures, and it'd be a shame to represent the entire franchise with just Slime who, in the main series of games, usually amounts to nothing more than just an easy obstacle to overcome. You can recruit it to your side in Dragon Quest 5, but I wouldn't say that's enough to represent the entire main series of games in a way that feels true to the heart of the series.
This is just my opinion, and I don't expect you or anyone else to agree with it. Sorry if this came off a bit rude, I didn't mean it that way. I just get a little sick of everyone thinking Slime is all DQ has to offer most of the time.
Dragon Quest didn't become iconic because of Slime. Slime became iconic because of Dragon Quest. It shouldn't be used to represent the entire main series as if it's the most important thing to come out of it.
Don't take this the wrong way, I don't hate Slime, and I get that it's the only thing those unfamiliar with the series recognize. That said, I feel like Slime would do that job just as well, if not better, being in the background of a DQ stage or even serving as the series' symbol.
That's honestly how I feel, and I'd be very disappointed if Sakurai chose to rep the series with Slime because of it. It's not a popular opinion, but I just needed to vent.