First, I'm not going to spell out strats, I'm only here to provide you with information. I don't know what your rosters are, or anything about your account, so I have no idea what you're working with. Also, this is not a loot thread, or a change stuff thread. there are plenty of other threads for you to talk about those things.
Tier 7 is different. It is a new fight. You should not think about it as T6, but harder.
The two major differences in this fight are the HP of each phase, and the boss's tenacity.
T6: 6/10/10/6 (millions)
T7: 2/4/4/2 (millions)
(These are rough numbers. I don't actually remember how much the T6 Rancor had, but those look somewhat accurate for each phase)
HUGE difference in HP here. Let's talk about it...
You do not receive any character resets on T7, so it actually makes sense that the HP is lower to account for this. If the HP per phase was not reduced, T7 would be out of reach for most of the player base, who does not have oodles of 7* characters sitting in the wings. This would be a bad move, as everyone wants to do T7 for those sweet, sweet, Han Solo shards.
Great, we've established that the devs are being kind to us ^_^
We're going to revisit the topic of HP after we talk about tenacity, as their relationship is very important in this fight.
T6: ~70% debuff/TM reduction SUCCESS ^_^ (probably a little more, I didn't see many resists)
T7: ~10% debuff/TM reduction SUCCESS >.< (maybe less, I stopped trying (characters with ~90%+ potency seem to land 60%+))
These numbers made me sad, as I'd just made Teebo AWESOME, and now he's benched. Oh well, I'll survive (so will Teebo, since he's on the bench, not getting his face eaten).
The relationship between the boss HP and tenacity is very important. You are no longer able to control the fight like you could in T6. This fight would be a JOKE if you could still manipulate boss TM like you could in T6 with his newly reduced HP totals. It is harder to get damage in because speed down and defense down no longer stick, he now acts with impunity, and eats your face. Oh, debuffs stick if he's been doored. I recommend sticking some stuff to him while he's doored (he's still going to eat your face).
Oh, he hits harder. He will eat your face.
A couple other things before we move on...
1. Escape starts on an 8 turn cooldown. He is absolutely going to devour one of your people before you can escape them. Luckily, you will probably not witness this, because he hits harder, and will eat your face.
2. You will witness him devouring your characters. Yeah, I said you won't, but I lied. The rancor's cooldowns persist through attempts, so... if you lasted 4 turns on your first attempt, devour will now have 2 turns before it comes off of cooldown on your second attempt. He is going to eat one of your toons. NOM!
Ok, back to the fight...
TM reduction not working like it did in T6, combined with the reduction in boss HP, means that your best option for survival is straight eHP. No more cute tricks with TM reduction to delay the boss from acting, or to stack LOTS of dots with TS. This combination turned the fight into a tank and try to spank fight. Try to DPS because he will eat the face of your glass cannons.
The secret to T7 is coordination. Unless you're all whales, and have huge rosters, you're not going to be able to zerg this fight for a win. Make a plan, take it slow. Observe what happens. Don't let people rush to get attempts in, play together. If you've planned well, I believe that a T7 kill is accessible to most guilds. I'm not saying that every guild out there can defeat the T7 Rancor, but... it's not only for whales.
Again, revisiting my 3rd paragraph... T7 is a different fight. If you bring your T6 strats in, you're going to be sad (unless you're whales and have large rosters to fall back on). T6 and T7 are difficult and easy in different ways. I believe that T7 is more difficult for non-whales, as I believe it requires more coordination (communication), and I'm not sure in-game chat is sufficient (we use Slack for chat). The actual fight and mechanics... I'm not sure that T7 is more difficult, but it is different.
A couple tips:
1. The door resets between phase 2 and phase 3. This means that you can immediately drop the door at the start of both phases.
2. Don't die.
3. Phase 4 is hard, he is going to nom on your people.
4. Phase 1 isn't terrible. It is still possible, with the right team, to do 15% - 20% of the boss's health in a single attempt. Phase 1 is getting a lot of hate from people, but it is actually the easiest to rack up huge damage numbers in.
6. You don't get character refreshes, but you do get two days. Take it slow, talk strats out with your guild.
7. I HOPE LEADER ABILITIES GET FIXED!
8. This fight will get easier once #7 happens. Not having leader abilities to create awesome squad synergies for phases 2, 3, and 4 makes this difficult.