Its not. Giveaway cards that don't at the very least convert gems from one type to another usually end up being utterly worthless for months (or longer). Things that go in the support role can be used without full stats, but stuff that is mediocre to begin with just essentially gets sidelined. But that isn't the worst part..
If the cards are on a once per-week rotation with a six week turnaround now and will eventually transition into kingdom troops where they come up once-in-gods-know-when (it'd be over six month rotation even now), and this is the only acquisition method, the problem is being able to ascend them, period, or even acquire them if you happen to, god forbid, miss a week. I'll have a major problem with it if this "competitive" mode ends up capping my kingdom stars and therefore my progress in the game, with, again, no way for me to move forward.
Basically, reasonable waits are fine and grinding is fine, but artificial walls suck. And since your guild has to participate in guild wars at least once every week where a new troop is featured to get at least one copy, this mode will be mandatory for progression eventually.