Note that the logical reads are the exact same and neither query is doing physical reads (the execution plans are the same– the optimizer doesn’t care what locks you are using). The queries were run with SET STATISTICS IO,TIME OFF and Execution Plans turned off, just to reduce influencing factors on duration and CPU.
The database engine is simply having to do more work here. Locking the pages in the clustered index is less work than locking each of the 1,825,433 rows.
Even though our locks are more granular, making queries run longer by taking out individual locks will typically lead to more blocking down the road.
Kendra follows up with several optimization possibilities, so read the whole thing.