If you don't want to spend more than 10-20$ per week (so if you are a player like me), just use your ingots to buy Jonin Medal and renew it once every 5-6 months, buy every month the monthly fee and spend the remaining ingots in try your luck and in 1 more SS convoy per day (if you are able to beat most of the plunders in your server) or in 1 more plunder attempt per day.

That will give you the highest coupons ratio possible.

Remember that investing coupons in a specific feature instead of another one fully depends on your relative levels, in the sense that is not said that using 2000 coupons in a feature instead of another one gives you the same outcome, but you can come here and ask us what is better for you to do step by step.

About your question: Yes, power overcome p2w ninjas. You can consider a p2w ninja like having a 10-15% advantage in power. In the sense, if you face a guy with p2w ninjas that is 50k power, usually with common meta teams at 60k power you own him (if you own initiative). Consider also that more or less every team has a specific counter team that can beat it with 20% less power and without initiative too.