opinions on the new defender tier list?

I don't think the ranking is bad.

The double weakness issue is a difficult one. Ice types are easy to get in my neck of the woods - Shelder is one of the most common Pokes and Seel isn't rare.

When Exeggutor is so vulnerable to Pidgeot, as well as being weak to Flareon (as common as Vaporean) not to mention Parasect (Paras are easily found round here) does he deserve to be that high?

I think CP has to be a factor too. Hypno is pretty solid, but he's going to sit at the bottom of a gym if he can even get in, whilst Rhydon could have nine defenders below him...

The fact that you didn't factor CP in your opinions says pretty much about why you disagree with some the list!
Yes, you may say Gyarados and Rhydon make horrible defenders. I 100% agree. But they have higher CP. Besides, they're both quite easy to acquire, so probably high IVs, which push their CP higher. High CP = high Gym placement. This adds great value to them as defenders. That's just how the game is designed.
Even a Tier 1 defender like Snorlax, could be taken down within a minute if he's at the bottom. So the true key to lasting longer is to stay on top.
Still not believe? Let me put it this way:
Say there's a Vape at 2800CP in the gym now, with 2 slots open. It takes ~30s to beat it.
If you put a 2600CP Lapras, a Tier 1 defender which takes ~35s to beat, you'll get kicked out in 30+35 = 75s, after the first round of attacking.
If you put a 3000CP Gyarados, which takes ~25s to beat, you'll get kicked out in (30s+25s)+ ReEntering Time + 25s ~ 90s.
Even though Lapras out-tier Gyarados, Gyarados lasts longer in reality.

All defenders have great counters that demolish them except Snorlax and Lapras.

Exeggutor deserve tier 2 for me, he is the one who hits the hardest with poliwrath. Bug type is weak, double weakness to bug is like having normal weakness to water. And even though he has many counters (pidgeot, fires, bugs, dragonite, lapras) he always end up dealing a lot of damage before being killed

I think this ranking is the most accurate they made so far. They eventually realized omastar wasn't the great defender they preteded he was.
I still disagree as well with venusaur (tier 3 for me).

Rhydon deserve his spot, he has to be higher to gyarados (better quick move) and golem (better stats).
You seems to forget that if not considering typing, Rhydon is as good as a defender as Lapras. He Deals more damage before being killed by neutral opponent than Snorlax.

I real would love that the position in gyms would be changed to pokemon level and not cp. Now cp is the most important factor if you want to stay in a gym. Also double weakness pokemon are easy to prestige against which actually makes them in some way better defenders.

I would base it even more on CP, in a high level gym position is pretty much everything and in a low level gym "good defenders" makes it harder to prestige.

The ranking is not bad, of course. The details depend on what is considered relevant. In example, I am pretty sure that Poliwrath and Slowbro are placed wrong. Poliwrath has no weakness that could be be exploited by any of the really strong attackers, while himself doing brutal damage. On defense he does actually better than Vaporeon, which is hampered by the bad performance of water gun. Slowbro on the other hand has one gaping hole in its defense: It is weak to ghost attacks. And by now everybody has at least one Snorlax with Lick.

What are your guys' thoughts on Omastar? I notice he's been moved down in this new list for defense, I wonder if its the same for offense. He was ranked high for both until this update.

Exeggutor is a beast. Double weak against bug? There aren't very many good bugs so who cares?

I disagree wholeheartedly with Chancey being best in the game. It can be taken out fast with lots of different attackers. Alakazam, dragonite, vaporeon everyone has, machamp.etc

Yo, I contributed to this list, so I can address questions and misconceptions.

Tiering is hard. There are several factors that come into play when picking defenders and deterring attackers. Some attackers care about potion usage and thus are deterred by heavy-hitters. Some attackers are deterred by long battles. In some areas, defenders have to have high CP to be viable.

For every defender, basically all that we cared about is how they fared against the big 4 attackers: Dragonite, Vaporeon, Snorlax, Rhydon. We also considered any worse matchups outside of those 4 if they existed. Usually, Dragonite was the most time-efficient and Snorlax was the bulkiest. We put more weight on the bad matchups because that's what attackers are more likely to use.

The issue of the double weaknesses is interesting. We found that defenders with double weaknesses were consistently underestimated by the community.

For example, Exeggutor is double-weak to bug. But it actually goes about even with Scyther, loses slightly to Pinsir, and demolishes Parasect. You are better off using Arcanine or Dragonite.

Rhydon is double-weak to grass and water. But Rhydon actually beats Venusaur. It loses to Vaporeon but does a lot of damage in return, better than defenders in a lower tier.

What we got from this is that attackers see a double weakness and overestimate the effect of that weakness, disregarding the actual outcomes.