Too much light in your render comes from HDR map not the engine itself. try different maps for refraction, rotate them play with them.
Jewellery rendering has been on here many many times already just do a bit of digging 
No point of looking for âbest engine of 2018,2019 and so onâ All (most) engines can give you pretty much the same output itâs only the difference in the way youâre getting to the result.
I personally use Thea render these daysâŚused to use Vray, Arion, Maxwell, Keyshot and few others.
Some examples here
PS. Donât ignore importance of your light setup and hands down tool to go is HDRLightStudio