Most of what you say is perfectly reasonable, IMHO. First of all... I guess I need to just say it out loud. He was a bad pick.
I can agree with you at all when you say that there is not even a reasonable argument for him progressing.
Now... I will respond to select points;
Let's not pretend the Knights were bad in Juolevi's D + 1 season.
In 2016-17 the London Knights had the 4th best regular season record in the 20 team OHL. There were only 4 points back of #1 overall and would have won two of the league's four divisions handily. They had the 3rd most goals in the 20 team league that season.
As for losing good players, it didn't keep his fellow defencemen from scoring more. Comparing 2015-16 (his draft year) with 2016-17:
Juolevi went from 42 pts in 57 games (0.737) to 42 pts in 58 games (0.724)
Mete went from 38 pts in 68 games (.559) to 44 pts in 50 games (.88)
Bouchard went from 17 pts in 43 games (.395) to 44 pts in 68 games (.647)
Im definitelynot arguing against Mete & Bouchard. They got better, maybe even passed OJ by.
I think just the fact that he is no longer exposed that ridiculous PP and still maintains his point pace is improvement in it self.
In the regular season in his D + 1 season Juolevi was the 3rd highest scoring defenceman on the Knights, 2 points behind Mete (same age, Mete played fewer games) and Bouchard (who was younger and played more games.) In the playoffs Juolevi outscored Mete and Bouchard by 1 point each, 8 to 7, with his scoring rate well below what it was in the regular season and in the previous season's playoffs.
In his draft season Juolevi had 9 pts in 9 games in the WJC and was considered a star. In his D + 1 season he had 2 pts in 6 games and was considered a major disappointment.
I watched all the games and felt he was among Finland's teams best players every game, and their best player the last game.
So what we have is Juolevi maintains almost as good a points performance in his D + 1 season as in his draft season while scoring at significantly lower rates both in the OHL playoffs and in the WJC. He was considered a star in his draft season and a disappointment both at the OHL level and in the WJC in his D + 1 season. His weaknesses-intensity level and lack of physicality-did not improve in any way. He was not better defensively.
Between his draft season and his D + 1 season Juolevi went from being the best defenceman both on a Memorial Cup winning junior team AND a championship winning world junior team to a 2nd pairing defenceman and major disappointment on a good junior team and on a disappointing WJC team.
There is no reasonable argument that Juolevi progressed between his Draft and Draft + 1 seasons.
I can't see any reasonable argument in favour of saying this is progression, much less the type of significant progression one expects to see between D and D+1 seasons.
It is reasonable to argue that he progressed. Again. The London Knights went from scoring 319 goals to scoring 289 goals.
That is a 10% dip in overall goals scored by the Knights. He still maintained the same point pace. I can't find TOI stats for the OHL but I think he was playing less on the PP. Bouchard pushed him for PP time?
I don't know if it was significant progression. Obviously he isn't projecting like his draft-position would lead you to expect. But still his team scored 10% less and he scored more then the year before.