Your Exeggutor is a really strong defender. I'd definitely keep it and even advice you to power it up.
I'd probably hold on with the Dragonites, as their IV's are not great and movesets are also not the strongest ones. That being said, they're still definitely strong Pokémon. Any Dragon Breath Dragonite is a good attacker and any Steel Wing Dragonite is a good defender. Wait until you see what you get from your Dratini.
Vaporeon is still a decent defender, Pokémon that counter Vaporeon are not that popular (at least not where I live in). Your Vaporeon has the strongest defensive moveset as well which makes it strong. Even though it's not optimal for offense, any Vaporeon is still a good attacker because Water Gun is just that strong.
Your Snorlax seems to be a bit on the lower CP side, how many candy do you have? The moveset is relatively strong though, not the best for either offense or defense but it certainly is a strong all-around moveset. However, because the CP is that low I might opt to save the candy and wait for one with higher CP.
Any Poliwrath with Bubble is a good defender. Even though technically Hydro Pump deals the most damage, people tend to attack Poliwrath with something that resists water already, so Ice Punch might give them a nasty surprise when they're trying to attack with a grass Pokémon (Ice is super effective against grass). Mud Shot Poliwrath with Hydro Pump on the other hand is a very strong attacker. Ground type has a lot of favorable match-ups (Poison, Rock, Fire, Steel, Electric), so even though the fastmove is not water type, you can still destroy Fire Pokémon with ease.
