This is a well developed melting pot archetype. It occurs in the later stages of a melting pot and will probably become the prevalent kind of 'shooter'.
Connor Betts is an outstanding example of the Nouveau Shooter.
The Nouveau Shooter is, like all of the other mass shooters, an individual reaction to a society's tendency to rely on false narratives for stability.
Because the false narrative of North America as indigenously white is discussed elsewhere on this site, and because it is also peripherally relevant here, it will be used as an example again here, even though he was not overtly reacting to that specific fiction.
Connor Betts is fringe by most standards, but what led to him becoming a shooter was the simple lack of true facts, a solid foundation, in his society. The important question regarding his 'fringiness' is whether it is a leading edge or a trailing edge, is he one of the last of a declining group or a leader of an increasing group?
He was raised in North America, but he wasn't taught North American history.
He was taught U.S. history.
The U.S. is certainly 'real', but it is a political organization, not a place. If you say "My ancestors came from the United States" you are saying "I have no base, no foundation, no history". This very problematic nonsensical worldview is being encouraged on young people for political reasons. In other words, it benefits political types in the very short term, but long term it is a developing catastrophe.
There have been a lot of comparable idiocies throughout history in which a small group of self appointed philosophical guides tries to conquer nature, conquer reality, by forcing a population to live in a bubble of lies.
When people in the U.S. are educated truthfully that the United States is, in fact, simply a political construct built on top of the geographic reality of North America then young people will be able to start perceiving realities accurately. Unfortunately that does not appear imminent, so Connor Betts is probably the leading edge of 'shooters whose concrete motive is obscure'. The normal tendency in society will be to create fictional psychiatric diagnoses to further obscure facts.
There is one commonality in melting pot mass shooters, a great example of which is
"Bourque’s parents were concerned enough about their son’s odd behaviour—his growing anxieties, the guns, his fanatical talk about perceived injustices—to reach out to retired friends in the police."
from the article
The goal of the melting pot, as Orwell pointed out, is to replace the family with the state, and most mass shooters recognize that at some level.
Another commonality is the similarity mass shooters have with cutters. Bourque's Facebook quote https://heavy.com/news/2014/10/justin-bourque-prison-sentence-now-parole-facebook/ is a common theme.
Three kinds of shooters mentioned on the mass shooting page are
a) 'far right' white nationalists who commit mass shootings modeled on nationalist or partisan 'soldiers', legends, etc and
b) 'rebel students' who commit school shootings modeled on 'authorities', usually law enforcers, and
c) converts to melting pot religions who model on perceived peers and historical melting pot 'heroes'.
Betts is not really in any of those groups, but he could be considered a 'post rebel student' shooter, somebody who, as a young adolescent modeled their relations on their perception of authority as 'law enforcement' in their society.
He had enough stability in his family to avoid becoming a school shooter as a kid. Then, as he aged, he never reconciled the conflicts that his family had helped him smooth over, and never found an authority to replace law enforcement as a model.
He was too smart to be a nationalist of any kind, and not gullible enough to become a radical Christian or to convert to Islam.
His choices were to either die quietly by getting a dull job in his father's footsteps, or to die making a lot of noise, like popping sounds.
Since he was at an age where loud noises are pleasant he chose the latter.
Stephan Balliet is definitely not in the 'nouveau shooter' category, but he overlaps in an important way.
Balliet, and most of the recent shooters, come across as bumbling, almost harmless except for the bullets. Balliet had a comedy of continuous errors in his 'attack' that would minimize the threat from those 'shooters' if there weren't some substance behind their ideology.
So the important question is, is there any substance?
Balliet, despite his ridiculous clumsiness, is humble as far as his mistakes go. He makes self effacing comments etc. That should be the first warning sign that there may be more substance to his ideology than is evident from his military 'skills'. Regardless any other issues that might be obvious, he isn't entirely motivated by ego or a small group of friends. His specific targets, Jews generally, then a Turkish shop etc, are silly, but also don't negate a possible bigger ideology that might be behind him.