FYI:

Jin reward comes in the mail, one half (participation) comes with exp, the other (top 10) does not. You can receive one without the other. So you should do Jin either way.

Nine tail exp reward scales with damage, with minimal amount of coupon and the magatama paid out as long as you participate. You can poke it gently with a lv 1 ninja to get the minimal reward for minimal exp gain. It may or may not be worth it but is a thing.

On the other hand:

You will, even if you do not skip exam, miss out on some reward from exam. As you gain power slower w/o leveling due to the other parts stated. As such, you will pass roadblock levels later than normal, thus missing out the amount you can farm out in between. This amount will only grow over time until such point where you should have cleared them all w/o freezing, at which time the gap begin to shrink, finally catching up as you, with freezing, clear it all.

Also to keep in mind, with increasing number of player freezing, the benefit is diminishing. Because you will lose to any one who started freezing in the same range before you did. And you will lose to ptw regardless. With in a particular level range, there is only a finite number of slots for "winners", at this point, you might not be able to grab a spot even if you did freeze. Unless, of course, you go ptw yourself. This will seriously depend on the level range you plan to freeze at as well as the server cluster you are in. You should investigate whether you will actually get the wins you want if you do freeze before hand.