Does Google consider the percentage of a keyword in your site as a
whole or individual pages more (I know they do this to some extent but
I think theme based websites are what is driving keywords now, not
individual pages)

For example:

If I sell widgets and "good widgets" is my keyword on my index page I
am targeting, but then on 20 pages in my site I do not talk about
widgets but "potato chips" I think Google will not rank me high for
"good widgets" even if my index page is well coded. All other things
being equal of course.