Formention is really not a need for the Flames. Moving Kylington for a non-top 6 winger is a bit counterproductive.

Kylington really also doesn't play RD

Plus the canada hockey investigation makes formaton have no value at the moment

That was mentioned in the description. I chose to ignore that as was mentioned

22 year old 18 goals, 32 points - he has top 6 potential for sure. Seems like a decent swap of similar situation players but we need a RD not a LD

His top 6 potential is the same as his former team Canada teammates in Dube. Kylington has already proven to be a top 4 defensmen. Calgary is contending, trading for potential is not the goal

Formenton is scoring at Dube's rate in his first full NHL season while being a year younger. Dube gets 58.6% offensive zone starts. Forms plays 3 x as much penalty kill. I would take Formenton over Dude any day. I get your point though and there's probably better options for a trade of one your dmen

Being 1 year younger in the D+5 and 6 year is fairly insignificant. Dube also severely under produced until the final few weeks of the season last year compared to his underlying numbers.
Formention had a 53.9% offensive zone start least year that's also a lot.
Playing more PK time is a silly argument considering how deep Calgary is at elite 2-way players and PKer's.

Compare their 5v5 play if you really want to choose one over the other
Dube vs Formention
From this it's pretty clear Dube was the far more effective player

Formenton absolutely has top-6 potential

He led the NHL in SH goals last year as a bonus