alt Hacker NewsRemember that the PC Engine came out in 1987, over three years before the SFC did. That makes Nintendo's CPU decisions even more questionable, but also explains the huge gap in graphics hardware - not just more background layers, but also effects like transparency, scaling and rotation, and richer colours.
Nintendo first demonstrated the Super Famicom hardware in November 1988: https://www.chrismcovell.com/secret/SFC_1988Q4.html . If you look at the hardware specifications listed, the only thing they changed between then and when it came out in 1990 is increasing the work RAM from 8 KB to 128 KB. I imagine they sat on the console for so long because the Famicom was still selling and they wanted to take the time to develop a good library of launch titles.