Heh, not at all. MUI was (and still is) an advanced and powerful GUI toolkit which just offers much more than other toolkits did at that time. ...
The original MUI isn't that heavy with basic settings. Of course it doesn't run well on 68000, but 020 or above isn't problem. MUI became quite a de facto standard on later days and you wouldn't have practically any Internet software without it, or pretty lonely with them at least 
It was a good thing for higher end Amigas and later days/future.
I must admit for me as a *USER* MUI was always a PITA. Bad performance with my 030/25 MHz days, always crashing somewhere etc. pp. And for having a nice and powerful *developer* GUI toolkit I as a *USER* should pay for a keyfile? No, never ever.
In the meantime my slowest setup is a 040/40 MHz and the crashing 3rd party modules problem is more or less gone. Nevertheless: If a software has a MUI and a Gadtools version (or even Reaction) I would not choose the MUI version.
