True, but if the explorer is somewhat more capable in combat and with an unique ability, you’d be more tempted to upgrade him in age 2 and actively use him in your army.
I don’t know about you but usually my explorer either idles somewhere I need vision or simply stays around the base after age 2.
serius ???
My suggestions ties these upgrades to the church card (which is a card commonly sent) hence none of the issues of delaying age ups are present.
ALSO the Explorer is excelent as a Meat shield or snaring in combat (and to detect invisiblw units) so it makes sense for him to BE buffed in a meaningful way without the need for a specific card