I just struggle to find a case for MacInnis over Forsberg in 2003, though I'm sure you watched more Western Conference hockey than I did.
to add to qpq's points, giving macinnis the hart is a "valuable" vote, not a best player vote. though, tbh, he was pretty close to both.
i followed the west more closely than usual that year, though i was living in non-NHL US market at the time so i only saw games when i could. but i did follow the conversation really closely, because that was the year that vancouver broke into the detroit-colorado-dallas-st louis hegemon. (those four teams had owned the home ice seeds in the west the previous five seasons, except one year that phoenix finished one and a half wins ahead of st louis.)
basically, macinnis was everything on that team and carried them to a 99 point season, the fifth seed, in a very competitive western conference (edmonton was the 8th seed, and would have been an OTL away from 5th in the east).
he was partnered with a rookie (barrett jackman, whom he helped to the calder) and his goalies were brent johnson and fred brathwaite. the rest of the d was alex khavanov, bryce salvador, jeff finley, and christian laflamme. pronger played 5 games. macinnis kept that team middle of the pack in goals against.
the offence speaks for itself. he was one point out of 30th in the league, led all defencemen in scoring, was exactly as dominant on the PP as you'd expect.
but defensively, every source at the time said he was lidstrom-esque. i don't want to diminish how polished and NHL-ready jackman was, because he was really impressive. but i think anytime a rookie steps directly onto a first pair and looks like a ten year vet, you have to credit his partner for simplifying the game for him and helping him look like that. and he played 27 minutes a night as a 39 year old. i guess you don't get bonus points for being old, but i don't think there was a more valuable player that year.
not to say forsberg wasn't awesome, of course. i just think if you replaced forsberg with, say, doug weight, that avs team is fine. if you replaced macinnis with, say, gonchar or hell forsberg's teammate rob blake, and that team is drafting eric staal in june.