Are you sure it’s the word counter that gives you trouble? I am not, because I made a test, and I can see that word counter generally does not re-count from start at each key press. I have recorded a screencast of the test, so you can see what I mean.
I created a new text document (0:02), then added a lorem ipsum text (0:04-0:07), and copy-pasted it to make 2000+ pages: first, copy-pasted the single lorem ipsum text up to 100+ pages (0:08-0:20), and then selected all the 100+ pages, and copy-pasted it up to 2000+ pages (0:21-0:37). Then I started to type, in the same time as Writer performed its word counter incremental update which was postponed when the copy-pasting work was being done (0:39-0:56); the typing lagged somewhat because of that, but it was not tens of seconds; rather, it was a matter of tenths of a second. And you see: the counter isn’t restarted each time I type a character: it continues from where it left last time. Then, at 0:57, I decided to open the floating word counter window; and when that window opened, it had “hung” Writer for some seconds (0:59-1:15). That was something unrelated to counting (because the counting resumed from where it left at 1:15). In the timeframe of 1:15-1:19, when the floating window caught up with real word count, I typed some characters, that only appeared at 1:19 (when the counter was finally up-to-date), and then, typing resumed normally, without delays, with ~instant word counter update.
So, presumably, what you see is a bug related to some property of your document (absent in my testing), and not something inherent into the word counting feature itself. I’d advise you to file a bug report about that to bug tracker, with the (anonymized) sample, rather that blaming developers for doing something (trashing the product) they didn’t do. Bugs happen; they need to be found (you have found one); reported properly (to bug tracker; we would be most thankful if you do), and then acted upon. Bashing is unhelpful.
