Psionicists is a mind magic-based class originally designed as THE Allod masters at "Crowd Control" although that role has been greatly diminished as of late. Due to removal of the conviction stat, changes to the willpower stat, and altering various mechanics in the game (nerfing reinc ability Fear, for example) Crowd Control psi has become a shadow of what it once was. There is no longer much return in investing so many talents and rubies into a dedicated CC build as a psi.
Damage-wise this class is among the best (if not THE best) at damage burst/acceleration although it does not have the top DPS ceiling potential of say, a full DPS-specced mage/warden/engineer/warrior/physical paladin/caster healer etc. If Allod classes were like cars, then psis would be the fastest at accelerating from 0-60MPH/0-100KPH but could not reach the top-end speeds other cars might reach. Single target and AOE damage can be quite good if you make the right builds, although a lot of psis will probably say they did not roll a psi to be a DPS player.
I would not say it is the weakest class but it might be the least played class at the moment. I believe recent trends have shown that other classes that were least played like scouts and engineers have actually jumped ahead of psis in terms of population. It does not help that psis are not the most friendly to level particularly to new players, and also due to the class mechanics are difficult to play and master.
People will still want a psi in the party if you are good and know what you are doing. However you will rarely be specifically sought after. You will see at endgame that most of the demand will be for skilled tanks and healers first and foremost. Then people are going to seek out bards/scouts/engineers for their fervor (health boost) and mages for their double Icy Grave CC. If you are a person who wants to feel highly sought after and courted and invaluable then psi is not the right class for you.
For leveling you don't have to mental link every mob. A lot of people tell me psis are tedious to level because they literally mental linked and killed every mob 1 by 1. The 20% DPS is nice, but if you invest in the standard DPS talents and rubies and keep your psi appropriately geared for every zone you can kill mobs quick without having to mental link. Mental link comes in handy for crowns or bosses, not only for the extra dps but also for the ability to mental twin to give yourself a damage buffer.
Some Random Thoughts:
- I would not suggest getting both Seal of Health AND Aura of Astral Power. You cannot use both at the same time. Sure, having the flexibility of switching between both buffs is nice but it is something that can be easily overcome if you plan out your parties carefully. Spending an additional 6 talent points or 3 rubies for a little flexibility is quite a steep cost in my humble opinion. Better to invest those 6 talent points or 3 rubies in better survivability or better DPS, etc.
- Investing in Exodus (psi version of the mage's sanc ability) is worth its weight in gold and definitely worth the cost of 1 ruby especially for the harder legendary astral sectors in endgame. I almost always do astral with my friend who is a mage and if the party is in trouble either one of us can save precious lives by teleporting the party to the ship if the other is incapacitated or dead.
- Mana Gift is a unique skill to psis that allow us to grant a caster party member 50% of their total mana pool back. I know there are mana potions in this game, but using that logic we don't need healers because there are also health potions in the game right? The fact is no one can plan for emergency situations where potions are all on cooldown or the healer is forced to spam mana-expensive burst heals because everyone in the party is taking massive damage. In long mob pulls/astral boss fights/raid bosses in difficult instances with the right debuffs/situations Mana Gift can make a real difference when the healer is running dry and struggling to keep the party up.
- Although AOE CC like TK Pull/Mental Pulse/Sonic Wave for psis is nerfed (can't stun for as long without Conviction) it is also a real difference maker for many situations whether in Astral or Dominion or Mausoleum of Sparks or wherever. In many situations it makes it easier for the other DPS in your party by grouping things together for easy AOE DPS or by stunning things long enough for tanks to regain aggro, healers to heal, DPS to cast spells, etc. These AOE CC don't heal your party per se, but they do damage mitigation and reduce the amount of heals your party would need otherwise. Every second you stun is a second less something can attack your party.
- I feel that the sentiment that psis are extremely "tanky" is severely overstated. Against equally-geared endgame people with similar CS items who know what they are doing, I actually feel quite squishy a lot of time (and I'm almost full fabled gear). Sure, if you queue for skirmishes and fight someone who is lower than you by several k GS it's going to be hard for them to kill you. But against well-geared folks who are both skilled and can communicate and focus-fire (like in Dominion) any psi can be quickly killed. The way a psi can be kinda tanky in PVP is using a 1v1 "Duelist" build where you max out survivability skills like Astral Body, Mental Twin, etc. and rubies that buff those skills, running high Determination, having more CS, etc. but then some of your DPS will suffer. Duelist build is just that, for dueling 1v1, and at best can extend some of it usefulness to perhaps party vs. party PVP. But in larger PVP like raid Dominion, Scarlet Bastion, Arena of Death, etc. it will be much less useful than a mass PVP oriented build and you will still die nearly as fast.
Sorry for all the text, but I kind of got lost in everything I had on my mind about psis as a class. I really do have a passion for this class and I want to see it thrive! Also I do not claim to be the sole authority on psis, this is just my humble opinion for my experiences being a psi. Apologies beforehand if any other psis find what I said unsavory, I have no intention to offend!