You assume wrong on all counts.
First, Aldridge is not "an undersized power forward". He's one of the biggest, (perhaps the biggest) power forwards in the league. Young is 6'8" 221 lbs. and was originally a SF, until he proved too slow to guard other small forwards.
Second, Aldridge is not "a worse 3-point shooter than Chris Kaman". Last year in Portland, playing for Terry Stotts, Aldridge was 37-105 from 3-point range. That's a very respectable 3FG% of .352 (the league average last season was .350). This year, Young was 7-30 from 3-point range for a 3FG% of .233. In Stotts' system, Aldridge was an average 3-point shooter. Young is a significantly below average 3-point shooter and has been his entire career.
Finally, Stotts tailored his offense around making Adridge the #1 option. Unless he suddenly becomes completely insane, he would never do the same for Thaddeus Young.
BNM