I don't know about poor design, since it seems to work well, but it is certainly a perfect example of German love of complexity. I greatly prefer the tensioner on the 603 -- almost exactly what you were wishing for!
A bracket, a spring, two bolts, and a shock. Nice and easy, except you have to pull the fan clutch to replace the shock -- the bottom bolt is about three threads too long to remove with the pulley on. I know, I tried.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!