What exactly fundamental work did he do?
GARCH idea is trivial from the point of view of time series. He just added an autoregressive term in equation and was lucky that volatility turned out to be persistent empirically. You know ARMA was invented many years before that and there were hundreds of other ARCH modifications after GARCH that were not empirically as convincingly successful.
Also, if Newey is not top econometrician, who is top econometrician then?
I think he did fundamental work in econometrics. We should not be too obsessed with new "ideas". To be an important contribution does not need to be a new "idea". Take Bollerslev's GARCH model. Published in JoE and has about 25,000 cites to date. Yes, it's not a new idea because it is related to an infinite order ARCH model of Engle (his advisor). You can generate GARCH dynamics by using an ARCH model with many terms. However, computation may become cumbersome. To conclude, I think Bollerslev's GARCH model constitutes an important contribution even if it is not a new "idea".
I agree that it is now rare to see JM papers that produces holistic contribution in econometrics. Let's be honest. Doing econometrics nowadays is much more difficult than it was in the 80s and 90s when the field was just born. More difficult in the sense that getting visibility and cites now is harder than in those years. Yet, I think there are JM papers that make important contribution. Also this year there were.