From what I see in cross server events, most f2ps who want to be competitive will use the water team with tenten, mei, and mabui and focus power as the ninjas required aren't as hard to get. If a f2p should save their coupons for a ninja, they sacrifice the power they would have got.

Some people focus on power so that they can be in the top percentage (20-25% at least) of players who can win in events such as sage since its level based. I find that the the lower percentage don't follow any strategy of power nor ninja.

You should also disclose what your level is and your friends'. Remember, they count level first when putting where you are in a sage bracket then power. It makes sense you need a higher power compared to the majority of the bracket to stand out. The lower brackets (lvl 70+) is when players start to understand the game and begin building their teams and build power. I'm like your friend who faces people with that power bracket. However, my friend, who is five levels higher than me and have a power difference of 7k), ends up in a higher bracket.

Anyways, in the end, just like what Armand__ said, research a team you want to play with and use your coupons wisely.