Nice interview! Yes, we had a three way war between the ST, Amiga and Arc fans in the later years. Arc fans always spouted out superiority, which in many ways it was, but the machines were expensive and lacked games support, with very few titles being written purely for the machine.
The Arc had a more powerful CPU, being one of the first ARM RISC processors, but it lacked a blitter and any kind of custom video hardware so it relied on the brute force method in many games like PC's of the time. There is a thread on it here:
It did have an internal PSU, hires 256 colour screen mode, high density floppy and 8-channel sound. It also had a very good RISC mulitasking operating system (first with outlined fonts?) built in that was easy to use and thus it's popularity as a school machine.
As for being 10 times more powerful - take a look at some youtube games on the machine and you decide. Nice machine, but not built primarily with games in mind due to the standard VGA like video hardware. Had it had some dedicated chips for gaming, it would have blown everything out of the water. Have to remember however, this machine was built on a limited budget and custom video hardware would have proven too expensive, which is a shame.