The issue isnt time investment, its artificial difficulty.

For example, Gegeruju with the swap rule.
If he swaps your best card for something weaker, might as well throw the game now, he's got 2-3 5 stars in his hand.
If he swaps a bad card for a 5 star, then you are in luck and may win.
Why? because the power dynamic is no longer one-sided.
Frankly NPC decks are tuned like crap. They are either super weak, or just OP.
There are a whopping TWO reasons why we win even 10-15% of the matches against the OP decks.
1. We can use the Plus and Same rules a lot better than they can.
2. The AI tends to make dumb moves.

The problem is, if we have no rules to exploit, the AI blatantly overpowers us.
I am still trying to get my 30 cards to unlock 2 stars. My hand consists of 4 cards who's total power is barely 15, and Bahamut.
I am playing against NPCs who's hands have 4 and 5 star cards, several of them, with power totals of nearly 30 per card.
Were it not for "lucky swaps" and the AI making bad moves, there is no way in hell that my 1 star hand could beat Gegeruju.
Mathematically (and realistically), if you were to play a HUMAN opponent who's hand was all but literally TWICE a strong as yours. you would be unable to win.
The only reason we win against these super decks is because of RNG and dumb moves by the AI.