I haven't witnessed it personally, but there's plenty of evidence on the internet that there were no shortage of harsh words spoken about the AVL engine 15 years ago, and they are still discussing whether the UCE engines have a proper thump, or whether an injector can truly be trusted to deliver fuel.
On the other hand, to the average observer, differences between the various engines and the various RE bike models are probably subtle indeed. Ask a die hard Harley guy whether the Pan, Shovel, EVO, or Twin Cam is a better engine and you will hear some very strong opinions. They are all air cooled, 45 degree, long stroke V-twins to me.
I think RE can be trusted to serve their market wisely. It certainly appears that the new twins are being well received critically, although the majority of sales in India are still the 350s. My guess would be that this codename J "redesign" is directed towards two goals, 1) meeting BS-VI emissions standards, and 2) reducing production costs. The existing RE bikes, as inexpensive as they seem to the US market, are still premium priced in India. To get a substantial part of the transportation market, RE needs to cut the price of a basic bike by something like 30%.