No, Tiagra is not better than Shimano 105, but they are not too far-off. A lot of high-end technology has trickled down to both Tiagra and 105 from higher-end groupsets such as Ultegra and Dura-Ace, so the two are pretty similar. However, Tiagra is a 2×10 group whereas Shimano is a 2×11 group. Also, 105 is slightly lighter than Tiagra because of lighter alloys that are used in its production.