Well, what I mean is a heavier racquet works very well for a classic, old school flat or lightly top spun eastern grip FH of the type most often found at 3.5 - 4.0 levels of tennis. It's also the weapon of choice for the classic 'block return'
And there is nothing wrong with that.
However, such players often lack the strength or technique to generate a lot of RHS through the swing path of a modern TS FH while using a heavy frame.
When trying this with a light frame, they tend to concentrate on the 'brush up' but without any RHS all you get is a looping puffball.
With a heavy frame, they can't do it at all so fall into the pattern of the flat line drive. (the use of the phrase 'full swing' is interesting here, I suspect you refer to a swing that starts at the back fence and extends outward to the target.)
In regard to serve, despite what TT posters would have one believe, most lower level rec players don't generate much pace or spin on any of their serves and simply getting the mass through the ball is their best chance of a solid serve.
however, I am sure many will disagree, and that's fine.
As for Rafa, maybe he is an extreme example, but go to a local futures touranment and see what the young guys are actually using... It sure isn't traditional 'player's frames'!!!
5.0 all courter. Dunlop Bio 400T with cyclone @ 50, Prince CTS Precision 90
"Tennis isn't easy" - Corners