Good IV Hypno or bad IV Exeggutor?
I have a 15/15/13 Hypno and a 12/6/2 Exeggutor, both around 1800 CP and Zen H./Psychic
Who's better for attack? Who for power him up?
It comes down to stat totals. For example, exeggutor has 232 base attack, Hypno has 162 base attack. Even if you add 15 points in IV for hypno, it still only totals 177 for his attack as opposed to exeggutor's 232 with a 0 IV. In short, a 100% hypno will never be as good as a 0% exeggutor. If exeggcutes are easily accessible though, I would wait for a better exeggutor. If it has to be one of these 2, it's hands down exeggutor.
Your correct in Long Term, but Wrong Short Term
Short Term: they are both at the same CP, they will have very similiar total Attack.
The difference is Executtor to be 1800ish is probably around a level 23 Executtor and the Hypno is Probably around level 29.
If you attacked a Gym with them both today, they would both preform about the same.
However, the Exeguttor has a lot more room to grow and is worth more powering up than the Hypno