Knowing the strongest Pokémon is not only based on the CP (Combo power) only, but actually from IV (Individual values) here is the total accumulation of attack, DEF, STM, load and height. If you want the strongest Pokémon, you can see it from IVs.
The following picture shows the comparison of Dragonite CP 3050 defense and Perseverance larger than Dragonite CP 3064. Because Dragonite CP 3050 has 100% IV while Dragonite CP 3064 has 82% IV.
Here is an easy way to find out IV, CP, Attack, DEF in Pokemon Go:
1. Download GoStats-apk.
2. Sign up Pokemon Go account.
3. In this GoStats application you can search for IV, STM, HP, CP, weight, Sweets in total, Candy cost, StarDust cost and Sweets that you need to develop Pokémon.
For iOS or PC users.
1. Then open the pogobag.me site using a browser Sign up Then use the Google account to get the authorization code Insert to the column Sign up pogobag.me, if you are a PTC user all you have to do is enter Username and password PTC account.
Good luck done.