Event Cards, successes and failures

I think this is some sort of back to square one kind of topic. What to do with a failure?

For those not familiar, a short summary:
The game in question is a war game where each region has a group of units. Infantry/Vehicles/Tanks. And they have a RPS system. So a mix is usefull in general. But when having a goal, you specialize some of your squads.

Event cards:
These can be played any time, any where, on any player. Unless indicated otherwise.

***

After play testing more and more. Especially in the games where you play with less units. Some Event Cards are rather... useless.
Other seem to be usefull only when you or your opponent apply a certain strategy.

The Event Cards can currently be put into 3 classes:
- Temporary upgrades. Good for one round, but used on an entire squad.
- Permanent upgrades. Good for the entire game, but used on just one unit or units.
- Changes in army formation, or direction in firing. Good for one round, but used on an entire squad. Backfires if this same squad is used a second time that round.

Your opponent(s) don't know what cards you have saved up. And thus they put their units in formation after declaration, but before the fight. The army formation change cards are played right after this. Thus still before the actual fight.

All cards can be stacked! Used on yourself, or your opponent.

***

The biggest failures are in the army formation cards.

Normally your opponent has only 2 to 3 different unit types in their squad. This was only discovered during all those play tests.
With just 3 different units, and some might have suffered damage.
The formation might be as followed:
1-ABC in the frontline.
2-AB in the frontline, C in the back. (Or A and then BC)
3-A in the frontline, B in the middle, C in the back.

The last one is already very rare. With every fight, you only attack the frontline first, untill it has become to small to protect units behind it.

Now, the Event cards that change formation, there are 5:
- Backdoor; you attack from back to front instead. C>B>A.
- Backdoor Advanced; you attack from the front and the back, and work your way to the middle. A and C, then B once A or C is to small/gone.
- Flank; you attack the middle lines first, you need at least 3 lines for this. If there are none, you attack the front first. B>A>C
- Flank Advanced; The same as Flank. But you still can attack the front line as well.
- Surrounded; All lines can be attacked. Not even one unit is safe.
- There are no Event cards that do the middle and back lines at the same time.

Backdoor and Backdoor Advanced, work great in the game.
Surrounded works exactly the same way as Backdoor Advanced. Unless there is a third line, then it is even better.
Flank is rarely of use. I actually used it once on my opponent instead, forcing him to fire on 1 particular unit that was placed in the middle.
Flank advanced has shown no use thus far. And even though I know of one way to abuse it just like Flank. That situation is still extremely rare.

***

When walls are used, I know that there will be one more line on average in most fights. But this too will be rare. These squads are mostly specialized defence groups. So still no need for Flank attacks unless the firing units are 1/3th of the squad or less.

In what other way could I improve the usage of these Event Cards? Flank and Flank Advanced.
Change their use a bit?
Or should I simply leave them out?
One way would be allowing the player to show these bad Event Card to others, and simply pick a second Event card that round?

I also want players to obtain more then 1 card/round. But 2 cards/round is too much. How to get in between with a fair but random way? Let's say, 3 players have after 3 rounds, each 4 cards.