Most people choose a road bicycle simply by the model of Shimano rear derailleur cause they can compare with other brands. But the most important aspect of a bicycle is the frame design and materials! Carbon Fibre absorbs rough roads better then most aluminum and chromoly steel is the best but can weigh a bit more then carbon fibre. So don’t choose a bicycle based on the rear derailleur! Case and point is the excellent late model bicycle the Jamis Endura Sport $1500 which has Tiagra Shimano components but the frame is full carbon fibre with a press fit BB 30
The frame on the Xenith Endura Sport has a butter smooth Carbon Fibre ride that is stiff, light plus comfortable for any rider with neck and back issues. Yes the rear derailleur is not high end but you can change that in the future for $100 slightly used on Craigs List.