No, it is not.
The ES is, more than any other Lexus model, the one enthusiasts love to hate because it wears its soft, non-enthusiast ride on its sleeve. Yet, it is more than competitive in the mid-size luxury sedan segment, outselling the German mid-size sedans (Audi A6, BMW 5-Series, MB E-Class).
(Data courtesy of https://www.goodcarbadcar.net/, Mercedes-Benz E-Class sales figures only available to 2016.)
Enthusiasts often use the sharing of parts and powertrains between the ES and the mass-market Camry to argue that the ES is a bad car. That is not good argument, in my opinion.
More and more automakers these days share parts, to lower the cost of development of new models. Lexus and Toyota are no different. Audi, part of the huge VW Group, is very well-known for sharing parts with other VW Group brands, including the cheaper brands.
And, yes, the Toyota A25A 4-cylinder is a buzzy engine but (and I don't have sales breakdown by powertrain) I would guess that the 4-cylinder AWD ES sells in very small numbers, less than the A25A Hybrid ES and much less than the 2GR V6 model. Anecdotally, I have yet to see any ES 250 AWD on the streets.
The sharing of parts and powertrains is not a problem; the problem is if the sharing is not well hidden, and having driven both the ES and the Camry, I would say that parts sharing is well-disguised in the ES, with its different suspension tuning and extra sound and vibration insulation. That is what has made it so successful in the luxury mid-size sedan market.
