In fact, if you go from 1980 to 1999, you'll find that either Williams or McLaren won 16 times out of a 20 years span.
You must be young if you think that one team dominating F1 is anything new. The only thing new is it's Ferrari, and not Williams or McLaren that is dominating.
That's a very superficial analysis. Just look at the number of wins Schumacher had in those championship years. Very few other drivers ever managed to come close to that number of wins in a season, and Shumacher's managed it several times. If you look at those other drivers, at best they managed to win half the races in a year. That's almost Shumacher's average, and he's done better than that.
When one driver and one team is winning 11/13 races out of a 15-18 calendar (depending on the year), then that is really dominating, and that's why there was all this panicked rule-changing when everyone was saying F1 was too boring because of Shumacher and Ferrari. It wasn't because Ferrari
seemed to be dominating and equalling past teams like Maclaren and Williams, it was because they were
actually dominating, and doing better on a race by race performance across the whole year. You would see Shumacher come across the line 30-60 seconds ahead of second place, after
slowing down in the last few laps.
Look at the numbers since 1980. These are the number of wins the world champion got while driving that team's car to the world championship:
Maclaren Championship race wins: 5, 5, 4, 8 (Senna),4, 6, 7, 8 (Hakkenen), 5.
Williams Championship race wins: 5, 1, 3, 9 (Mansell), 7, 8 (Hill), 7
Benneton/Renault: 8 (Shumacher), 9 (Shumacher), 7
Ferrari: 9, 9, 11, 6, 13 (All Schumacher).
You suggest looking at the last 20 years to see that other teams and drivers have dominated F1 in the same way as Schumacher/Ferrari. I contend that those stats show the exact opposite: Schumacher/Ferrari have dominated
more.
BTW, I'm not that old, but I do remember watching the cars go round with turbos, ground effect skirts and (later) active suspension before they were all banned.