Lots of problems you're having here just stem from a lack of understanding of Dota mechanics, which I admit are often not well-explained by the game. Thankfully, the community has a bevy of info out there if you're willing to learn.
For example, tower aggro:
Gold loss on death is a feature that encourages aggression early and often, but it is also something that can be managed by the player because there are actually two types of gold in Dota: Reliable and Unreliable. Gold you gain passively, from creep kills, and from selling items is unreliable. You will lose a percentage of this gold when you die, so good players often play attention to this ammount and spend their unreliable gold ASAP in tough games (if you scroll over your gold, it breaks down what amount of reliable and unreliable gold you have. When you spend gold, unreliable gold is used up first). For heroes who often build a very expensive item as their first major item (Naga, Lone Druid, or Spectre often get a Radiance after their boots, which has a component that costs 3800 gold), dying is a huge setback to them.
As for the bit on Riki and Sniper's ultimates, I have to be blunt: Get good. Those heroes are among the worst carries at even average MMR. Riki kind of sucks at farming (his steroid doesn't even work on neutrals, since they will be facing him while he's killing them), so he often relies on snowballing off of hero kills. He's not like an Anti-Mage or a Naga, who get way more out of a few minutes of farming than most other heroes in the game and suddenly become powerful without having even fought you. Riki relies on you being unprepared. Sentries placed in crucial locations will spot him and maybe even allow a counter-gank on him. A Force Staff or Ghost Scepter (which you should be getting ASAP if you're squishy or a support) will severely hamper his ability to solo kill you, and those aren't very expensive items (~2K and 1600, respectivley). Sniper's ultimate is dodgeable, interruptible, and relies on you being somewhat out of position for him to get a kill on you with it. If you're against a Sniper and you're at low HP at the end of a teamfight, get to fog ASAP or just teleport out.
I'll admit Dota does a bad job of teaching deeper mechanics, but the info is out there. And honestly, if you don't know these things, then the people you're facing likely won't either. You don't have to have an encyclopedic knowledge of the game when you're new. Learn as you go. You'll eventually get to the point where you understand things like damage types, situational item builds, when to ward where, and the specifics of hero matchups. And if something really bugs you, look it up and try to see what you can do to get better results.
For example, tower aggro:
Gold loss on death is a feature that encourages aggression early and often, but it is also something that can be managed by the player because there are actually two types of gold in Dota: Reliable and Unreliable. Gold you gain passively, from creep kills, and from selling items is unreliable. You will lose a percentage of this gold when you die, so good players often play attention to this ammount and spend their unreliable gold ASAP in tough games (if you scroll over your gold, it breaks down what amount of reliable and unreliable gold you have. When you spend gold, unreliable gold is used up first). For heroes who often build a very expensive item as their first major item (Naga, Lone Druid, or Spectre often get a Radiance after their boots, which has a component that costs 3800 gold), dying is a huge setback to them.
As for the bit on Riki and Sniper's ultimates, I have to be blunt: Get good. Those heroes are among the worst carries at even average MMR. Riki kind of sucks at farming (his steroid doesn't even work on neutrals, since they will be facing him while he's killing them), so he often relies on snowballing off of hero kills. He's not like an Anti-Mage or a Naga, who get way more out of a few minutes of farming than most other heroes in the game and suddenly become powerful without having even fought you. Riki relies on you being unprepared. Sentries placed in crucial locations will spot him and maybe even allow a counter-gank on him. A Force Staff or Ghost Scepter (which you should be getting ASAP if you're squishy or a support) will severely hamper his ability to solo kill you, and those aren't very expensive items (~2K and 1600, respectivley). Sniper's ultimate is dodgeable, interruptible, and relies on you being somewhat out of position for him to get a kill on you with it. If you're against a Sniper and you're at low HP at the end of a teamfight, get to fog ASAP or just teleport out.
I'll admit Dota does a bad job of teaching deeper mechanics, but the info is out there. And honestly, if you don't know these things, then the people you're facing likely won't either. You don't have to have an encyclopedic knowledge of the game when you're new. Learn as you go. You'll eventually get to the point where you understand things like damage types, situational item builds, when to ward where, and the specifics of hero matchups. And if something really bugs you, look it up and try to see what you can do to get better results.
