That only seems to work. As I pointed out (later than this question) in How to enable Control key combinations for GNU screen on putty?, the difference when you do not modify
screenrc is that the terminal description for
screen sets application mode for the terminal.
However, applications running in screen using this workaround can send escape sequences that screen does not recognize. Using
infocmp putty screen
to see, these include
hpa (horizontal position absolute),
vpa (vertical position absolute),
indn (index by a given number of lines), and
rin (reverse index by a given number of lines).
Not all applications will misbehave (i.e., those which do little optimization of the screen output will "work"), but ncurses would use those features.
However — since you have the
putty terminal description available, that implies you have the full ncurses database. If you set
outside screen, then screen will use the terminal description
screen.putty, which does what you want.