OK, numbers for previous podium finishes in GT's for top 5 finishers in Tours 2012 - 2016.
2012 - 7
Wiggins - Tour 09, Vuelta 11
Froome - Vuelta 11
Nibali - Giro 10, Vuelta 10, Giro 11
Van Den Broeck - Tour 10
Van Garderen - N/A
2013 - 9
Froome - Vuelta 11, Tour 12
Quintana - N/A
Rodriguez - Vuelta 10, Giro 12
Contador - Tour 07, Giro 08, Vuelta 08, Tour 09, Vuelta 12
Kreuziger - N/A
2014 - 11
Nibali - Giro 10, Vuelta 10, Giro 11, Tour 12, Giro 13, Vuelta 13
Peraud - N/A
Pinot - N/A
Valverde - Vuelta 03, Vuelta 06, Vuelta 09, Vuelta 12, Vuelta 13
Van Garderen - N/A
2015 - 26
Froome - Vuelta 11, Tour 12, Tour 13, Vuelta 14
Quintana - Tour 13, Giro 14
Valverde - Vuelta 03, Vuelta 06, Vuelta 09, Vuelta 12, Vuelta 13, Vuelta 14
Nibali - Giro 10, Vuelta 10, Giro 11, Tour 12, Giro 13, Vuelta 13, Tour 14
Contador - Tour 07, Giro 08, Vuelta 08, Tour 09, Vuelta 12, Vuelta 14, Giro 15
2016 - 8
Froome - Vuelta 11, Tour 12, Tour 13, Vuelta 14, Tour 15
Bardet - N/A
Quintana - Tour 13, Giro 14, Tour 15
Yates - N/A
Porte - N/A
What stands out the most using this metric is just how phenomenal the field was in 2015. But 2014 does OK in this comparison as well.