First, I totally agree about templates in pathfinder. (Although thee Class-Simple Templates are awesome, they let you add class abilities to monsters without giving them all the the class, just the essence.)
Just tonight I ran an encounter that had a pretty awesome tank.
So a party of 5 level 6 players are riding a very large train through a magically contaminated wasteland. Because role-playing they know something is going down related to the sixth car today, so half of them are investigating the car, while the other half are doing an "Safari" of sorts with several other NPC's and shooting at various mutated wildlife with guns. (Industrial Revolution Era Game)
Suddenly the train sequels to a stop! (Acrobatics for the people on the roof) The bridge ahead has been barricaded. A massive (gargantuan) Hydra like creature with five heads, but seemingly made of shadows raises from the humid swamp on the left side of the tracks. (The right side is a glacial plane of Ice). The Screaming Malice(Hydra) begins attacking the train cars, after an attack it's head breaks off in the car, then the severed head turns into a new mini drake enemy (CR 2) with 10 hp (taken from the Malice's Max hp), and the head regrows on the body instantly.
Now the Malice has an AC of 26 (~30% hit chance for our martials), but it's Touch AC is 04 (Guns and Spells(Remember the Safari shooting))
It has 300 hp (Though each spawn will be taking 10) it also has 5 attacks for a ridiculous amount of damage each. But it uses it's attacks mostly on passengers (it's size lets it hit more than one square). The bonus condition is keep most of the passengers alive.
The cool part though? This is all a distraction, the monster was lured by some bandits native to the Wasteland. A round after the monsters appear, the bandits attack the front of the train aiming for Car 6. The train's guards can (hold off the bandits, or distract the hydra) for 3 rounds(whichever the party does not do). The bandits are a CR 10 encounter in total, Very Difficult, though the party does have allies.
The party actually, due to location ends up fighting both at once. It is a long and thrilling encounter in which the natural attack specialist downs 7 of the Spawn drawing an attack from the hydra which crits, nearly lethally in one shot, and takes an arm and a wing from him. Fortunately at 50% hp (from an ally's attack immidetally afterwards) the predator flees, and the Warrior survives.
The fight against the bandits is tough, the party is split and only 2 people are here to fight, but careful use of allies, cover, and well timed AoE spells swing the incredibly difficult fight into their favor.
There are many losses, several passengers have died, many of the guards lie dead, our Warrior has lost two of his limbs and the ability to fly. But, battered, bloody, and bruised they are victorious. Flush with the realization that lesser men would have failed, they are Triumphant.
Not every encounter need be so harrowing, or so Epic. But it is what I look for when it comes to combat.
And! It is imo a good example of a tank in Pathfinder, plot-wise, the Hydra was not relevant to the fight, but they could not ignore it or else the passengers would die and possibly the entire train would be destroyed. Bu tit served to distract them, and force them to split their resources, or make a difficult decision, the encounter would have been much easier if they had decided to focus on the Bandits and let many passangers die, or focus on the Hydra and let the bandits steal cargo. They made the hard choice, and they paid for it, but they are also rewarded for it.
In my opinion, the purpose of a tank is to force the party to make a choice.(Spend resources on the tank or suffer the consequences) It is not like a tank in an MMO, because in an MMO the tank has Agency, in D&D you should consider the player's Agency instead.
Another Example of a tank might be a Scarred Witch Doctor, While individually they character is not offensive, they specialist in having a ton of hp (and generally massive defenses), and debuffing. Every round they are conscious, they are making it harder for you to fight the other enemies, but to get rid of them requires significant resources. However, much like the hydra's Touch AC of 04, the Witch Doctor is vulnerable to Reflex Save spells that disable them and being grappled. I would use this character against a part that has one of those, and the character will feel empowered for being able to take care of the threat that nobody but them could deal with, easily.
I still think 5e is pretty good btw, it has the flexibility to allow a lot of what I like in my games. That is not something I can say about 4e though.