This is true. He is only mentioned in passing, rather than being present. Although, if we look at game dialogue and the DR wiki, we can gather clues about who DR Azzy is, concerning personality...
(You opened the door with your eyes closed. You saw nothing.) Attempting to peek into Asriel's room in Queen's Mansion Asriel, a returning character from Undertale, is Kris's older brother in Deltarune. He is mentioned by numerous characters in Hometown, but is away at university and does not...
deltarune.fandom.com
-Azzy seems to be friendly with the townsfolk, and seems to be well-liked and popular, which is unlike Kris. This means unlike UT Azzy, DR Azzy isn't a controversial figure, but rather is well-liked all-around.
-He has trophies in his room. He's probably involved with sports or some kind of other extracurricular activity.
-He loves religious ska and was a part of the church choir, telling me that he was also beloved in his church community and loved attending services as well.
-He would take Kris out for hot chocolate after services on Sunday after Toriel and Asgore separated.
-He would carry Kris to school if Kris woke up late.
-He and Kris to be fans of Super Smash Bros. or at least the DR equivalent, called "Super Smashing Fighters".
-Catty seems to be very attacted to him, but he seems to be more neutral in turn.
-He's a college student, attending a university.
Knowing all of these facts, here's what we can gather about Azzy.
1. He's popular in general, meaning he has to be doing something right.
2. He's involved in extra-curriculars and seems to keep himself busy. He's not one to get bored.
3. He's clearly religious and actively involved in his church community before going off to college, meaning he has good rapport in more niche areas of the town as well.
4. He loves Kris a lot. Asriel is the big brother that Kris needed, taking care of them throughout all of their years growing up together.
5. He could be attracted to Catty, but isn't nearly as attracted to her as she is attracted to him. He's taking things slow, or is perhaps even neutral and sees her as "just a friend." This would show that he's not really invested in romance, or alternatively works through romantic situations carefully and slowly.
6. He's 18-22 in age.
While we don't know a LOT about Azzy, I would argue that we have at least a baseline to start out with. DR Azzy, as opposed to UT Azzy, isn't a character who's life is filled with tragedy like UT Azzy. Neither did he go through "resurrection no jutsu" and end up in an alternate body. Rather, he fills that "wholesome kid from up the street" trope who loves his family, loves God, and loves sports. There's still plenty of work that can be done with his character, and plenty of potential that I hope is fulfilled.
However, I will say, if Kris IS breaking bad like we're led to believe at the end of DR 1, it's a good direction for Kris' character to take if he wants Kris to play the foil to Azzy in one way or another. The foil comes into play when one character's life is one that is going well and he's well-grounded; everything's working together well. But with Kris, on the other hand, with ripping out their very own soul and flashing red eyes, while dawning the knife... things are very ominous on Kris' end, on the other hand.
Sibling vs. sibling... one who takes an innocent path, while the other takes a dark path... it's a very neat foil to have. I think it would be cool if Azzy ends up being a boss fight for Kris. That would be neat. Or, have them play foil to each other at least. There are a lot of possibilities there, but the ones I named, I think have the most potential and make the most sense.
Awesome clean reference sheet! :D
