I see the dis-similarities with more focus.
(1) they didn't shoot up their school.
(2) they never mentioned any enemies they had at school as a motivation.
(3) they were absolutely silent as to their motivation up to the end.
(4) unlike Eric and Dylan, who were born blabbermouths, K and B maintained a curtain around themselves that few appeared to have pierced.
(5).. Eric and Dylan had a fixed target. They passed other people to get to the agreed upon target ( the other kids at school )
(6) K and B had unfixed targets, honing in on those who inadvertently crossed their path.
(7). the big one, in my book. E and D were focused on people they knew, members of their own community, causing the maximum spread of revenge right across the board where they lived and died.
(8). K and B chose to skitter on out north, far away from Port Alberni, out among strangers , far away from people they knew, not wanting to conduct their program among the community they knew.
(9). E and D got it all over with quickly, in comparison to K and B , who took their sweet time about it, and that means , to me, they had a certain set of circumstances for killing that had to be met for them to launch into the murdering. K and B strung it out for days. That had to be significant to them.
(10) their final words of K and B , if such it can be called , was brief, minus all the rantings and ravings of racist, ageist, genderist bollocking that E and D spend an inordinate amount of time on, relative to the crime they were about to commit.
(11)… in the middle of killing, in fact, between the killings of Mr Fowler and Miss Deese, both K and B rang their parents and put on a performance that, as usual , went right over the heads of both fathers. It was so good, giving no hint to the parents that they were conversing with murderers , and achieving a few more days of non scrutiny. E and D didn't do this, this last contact with reality. I regard that as deeply significant, also.
and so much more.