To be fair, when this card first shows up in real life, CyDra is a very common card (2000 DEF means nothing when your opponent has 2100 ATK) and Spikeshield doesn't exist yet (in fact it wouldn't exist until like maybe 10-15 years later)
The only kind of scenario this effect is ever useful for is poking someone with Black Stego without leaving it vulnerable. I guess it technically makes it less vulnerable to cards like Stop Defence, too, but given most of those in Duel Links are things like Enemy Controller they could just use after Stego changes to Defence, that isn't helpful.
Anoymous
Airmani