Uhm. No. The Amiga 500 is a 1987 design verses 1990 so you're already comparing Apples to oranges again. Compare an A500 motherboard with a Macintosh SE and your thesis pretty much falls apart. About the most you can say is the Mac SE's board is more compact but, likewise, it *mostly* does less. (*Video and sound systems are far less sophisticated on the SE, but it does include a SCSI chip while a mass storage controller was an add-on for the A500.) Both consist of a handful of LSI chips, mostly through hole, tied together with DIP-package 74xx logic and PALs. About the only thread you have to hold onto here is that Commodore didn't bother doing a "500CR" switching from through-hole to surface mount in 1990; going to surface mount waited until 1992.
And, yet again, the question to be answered is: so what? Surface mount certainly has its advantages over DIP; it tends to be more reliable and allows somewhat more sophisticated automated assembly techniques but a computer built either way can work equally well. Using a less sophisticated assembly technique does *not* make the A3000 a less sophisticated computer than a contemporary Mac. The best explanation for why the Amiga stuck with the less modern assembly techniques undoubtedly comes completely down to financials: Commodore was seriously struggling by 1990 and probably didn't have the money to retool their assembly lines while Macs sold in much larger volume with *huge* profit margins, making it trivial for Apple to push some of those profits back into constantly redesigning the same old computer to save a few cents here and there during manufacturing. (And make no mistake, there was absolutely *nothing* innovative about the Classic/Classic IIs other than how far they pushed the envelope in the field of cynical cost-cutting.)
Anyway, I guess if kicking a dead dog makes you feel better have at it, but I'm still totally missing the point.