Donphan?
So I'm a little confused to not see Donphan defending in arenas. He's the pokemon with the #8 highest CP, is rated as good defender by gamepress, has a solid moveset and in comparison to other ground pokemon such as Rhydon and Golem doesn't have a double weakness to water and grass. So how comes he isn't in gyms? At around lvl 30 he should be around 2650 CP, so he would probably be in the lower half of most gyms, but still would be uncomfortable to fight against and bring a little diversity.
I have evolved a hatched Phanphy at 93% with Counter/Play Rough and am tempted to push him to lvl 30+.
Answers
If you want to stay in a gym as long as possible and you are similar in levels to trainers around you, #8 CP, IMO is just not high enough...His max CP is also substantially lower than Vap (135CP) where unless you are much higher in level, will be knocked out super fast...(within 1 or 2 days).
He also lacks a STAB quick move and his STAB charge move is only 1 bar...
I've hatched two Phanpy and caught one wild. I haven't checked, I might have enough candy to evolve, but nowhere near enough to power up to a respectable level for placing in gyms.
http://www.pogomoves.com/check.php?lang=en&pkmn=Donphan&basic=Counter&charge=Play+Rough
Also, looking at damage output, there is a pretty big drop off in defensive damage if you get Tackle instead of Counter.
I've hatched I think 4 of them so far but I don't have enough candies to get him high enough 2600+ to get him a decent spot in a gym. Once I have enough candies I will get him to 2800CP and definitely put him in gyms.
He might not be the best defender but he's cool looking and I'm definitely powering one up to put in a gym, regardless of the moveset.