I am so glad I am old enough to remember the 1989 team well. If they play under current rules, the 1989 team may score 100 points. Seriously.
When it comes to comparing teams in different eras, I prefer to compare them to their contemporaries. The 1989 team dominated at a level never before seen.
It is pointless to use the whole today's athletes are bigger, stronger, etc argument. If we are going to pull out that argument, then there would be no need to compare teams in any sports across eras because the nod would always go to the more recent team. It would make the 2012 Jacksonville Jaguars better than the 1964 Cleveland Browns for example. Sure the athletes are better, but if we are ranking the greatest teams in NFL history, no one is going to get on their soapbox and argue that the Jags are better