We can build amazing things today too, but we have a lot higher standards and a lot more requirements than they did, which makes everything take longer time. Outside my office window an enormous new new warehouse was erected in just a few weeks, but it is just a huge box with no added extras so it can't have been very hard to do

One thing that changed is that modern engineering moved a lot of complexity from the construction site into the design phase. A project today may take longer because we simulate, certify, model failures, and optimize before pouring concrete. The old projects sometimes had more visible physical labor, but less computational overhead.