Acquiring character shards, active and inactive requirements are different.

Upgrade Star Level Cost
1* = 10 (technically an unlock, but equal in cost)
2* = 15
3* = 25
4* = 30
Now, if you do a little math 10 (1*) + 15 (2*) + 25(3*) + 30 (4*) = 80 (shards to upgrade a character to 4*)

Unlock at Star Level Cost
1* = 10
2* = 25 (10 for 1* + 15 for 2*)
3* = 50 (10 for 1* + 15 for 2* + 25 for 3*)
4* = 80 (10 for 1* + 15 for 2* + 25 for 3* + 30 for 4*)
The end result is unlocking a hero at 1* and then upgrading them to 7* will cost EXACTLY the same number of shards as farming 80 shards to unlock a hero then upgrading them to 7*.
The only way to get heroes at cheaper shard cost is to unlock them from card drops.