Your last coment is incorect, If you go by the old tech of the roots blower there is some merit to what you say. However the roots blower people havent been standing still either! There have been alot of advances in root blower tech that has raised the efficientcy of the roots blower well above what it used to be. Flexabilaty? How do you mean?
The majority of turbo's used today operate well into the mid 70's as far as efficenty is concerned ... superchargers are lucky to hit high 60's and roots are lucky to see mid 60's (if that's even possible). Sure, you have instant boost, but what happens when you want to up the boost? You have to jump through hoops with special tools to up the boost. This can take hours ... 1 to 1.5 for a great mechanic, whereas with a boost controller, turbo's can be reboosted instantly! Some chip makers support mulitple programs that involve a "secret" sequence of inputs at startup to switch from one program to another (valet, 91 octane gas, 93 octane gas, 104 octane gas, ect.) ... physically not possible with a supercharger since it must be driven by a pully.
Maybe one day 100 years from now when they invent the infinetely variable sized pulley
