Thing is, they could be avoided by a skilled player by either avoiding known sniper positions or doing good spychecking, while the impression I get from a lot of Overwatch videos and my limited playtime is that a lot of the ult abilities are unreasonably difficult to avoid.
Well there's 21 heroes so yeah, knowing all of their abilities and ultimates (and how to avoid them) is pretty knowledge-intensive. It's not like a top-down MOBA where you can see pretty clearly what's happening, a lot of the time you're killed from miles away by a target that was either above you, behind you, or everywhere at once. Of course the Killcam does help with this, but it'll still take a long time to figure it all out.
The ult abilities sometimes just make the game stupid. I'll give 3 examples from a recent game. So this was an "Attack" mission for my team, and a "Defend" mission for their team. The objective is simple enough, all you do is capture a point by standing on it. The more people you have standing on it, the faster you capture it, and the enemy team does their best to prevent this from happening.
Well, there's a lot of heroes in the game that make attacking a point a living nightmare. The Dwarf Engineer character with the turret is tough enough because the turret has an unlimited range and is perfectly accurate at all ranges (no turret rotation speed), meaning that if he places it correctly it can cut down your team from miles away while being almost impossible to hit. However, getting close to it means getting close to his team who of course are going to be defending it. Then Bastion who can turn into his own turret/gatling gun has a similar strength/frustration but it's at least a little more balanced since he presents a bigger target and the player actually has to aim. Finally, Roadhog who puts these bear traps on the most common flanking paths which can trap several people at once. He also has the demo grenades like in TF2 and sticky mines that he can detonate manually.
So all of this is hard enough to circumvent. Oh don't get me wrong, if you were a professional team who were super coordinated and knew all the counters to this stuff it would probably be a piece of cake. But playing with 5 other random players...It's tough because any one of those characters can kill several of you on their own with ease.
However, the real frustration comes when your team finally does gather the necessary coordination and momentum to finally capture the point. Sounds great right? You're all on the point and life is good, now you can win. OH, except did I mention that these 3 characters who were hard enough to deal with before now have their ULTIMATES ready, and are about to anally assault you in the most gruesome and terrifying ways imaginable.
The Dwarf Engineer's ultimate heals all of his health and gives him like 800 armor, basically making him invincible for the duration of like ten seconds. It also upgrades his turret to level 3 and make it near-invincible. The level 3 turret in Overwatch is pretty much same as it is in TF2. It has rockets and it destroys everything in milliseconds. Except in TF2 you can kill it pretty easily, but in Overwatch it's invincible while temporarily upgraded. So basically, he's god mode (both his character and his turret) for ten seconds. On his own he could easily wipe out a team.
Then Bastion's ult heals all his health and turns him into a tank (not figuratively, a literal tank) whose shots do massive aoe damage and can also easily destroy an entire team attempting to capture a point. He's fairly difficult to kill as well in this mode and can fire about once per second.
Roadhog's ultimate allows him to, from afar (a place he can't be attacked) create a mobile, guided bomb which he can then manually steer to a location only for it to explode and deal incredible (read: team killing) aoe damage, pretty much wiping the entire enemy team off of the point immediately just by exploding it in the middle.
So by the time your team finally does gain the coordination and/or luck required to take the point, the enemy team just pops all of their ultimates and you're all instantly wiped. Keep in mind I just listed THREE. They still have 3 other team members with their own ults so good luck.
Of course you have ults too, but you will have probably already used them just to get on the point, and since ults are generally better at killing enemies than protecting yourself (with a few exceptions) they aren't much going to help you survive the inevitable onslaught.
One final nail in the coffin is that these ultimates, while incredibly frustrating and overwhelmingly awful to deal with, are always off cooldown again by the time your team has finally gathered its wits and coordination to take the point again, leading to a feeling of utter desperation and hopelessness because no matter what you try, it seems impossible to even think about winning.
Which in general makes defending in Overwatch a lot more fun than attacking. I've been told by a friend (who I trust) that in high-level competitive play, attacking is actually considered the easier objective, and I wouldn't necessarily doubt that if your entire team was well-balanced, well-coordinated, well-practiced, and using some kind of VOIP program, but with 5 random players? The ultimates often make it feel insurmountable.
Symmetra is a really good character (one of my personal favorites), but her abilities make her much more useful on defense than offense. She's almost useless on offense because she has these miniature turrets you set up on walls, however each one takes a couple seconds to set up (which in a game like this is an eternity), and you have to have 3-4 for them really to be useful. They're also pretty squishy so you want to set them up in an area beforehand, which is perfect on defense, but very non-realistic on offense. She also has a shield which you can place on allies, though it has a short cooldown. This is much easier to do on defense as all your team is usually gathered in an area, than on offense where everyone is moving around quickly attempting to attack from multiple angles.
So yeah, Symmetra is great on defense, her ultimate (portal) allies teams to travel to the objective almost immediately, but she is almost polar opposite on offense. Even if her portal is still useful (maybe even more useful), the rest of her kit doesn't work very well.
