I enjoy playing Phantom Lancer but I feel that I have no idea how to make him threatening until late game.
Well, that's the thing. Carries (especially hard carries) aren't threatening until late game. That is literally the entire point of the role. They can't do anything early but if you let them get farm and the game goes late they'll wipe your whole team. If you want to be threatening early, you should pick someone like an initiator or a ganking mid (I know you said you hate mid, but, well, if that's the hero role you want to play...).
I know you said you liked Tide... maybe try somebody like Slardar? He doesn't have the screenwide aoe ult, but he does have a small aoe stun, and he can be threatening as a rightclick hero if you get early farm and decide to build him that way. That's what I meant on your other post when I said "you'll start knowing how to make decisions on hero/item combos based on how the game is going." If you notice you're losing teamfights due to positioning and your team needs an initiator, you can rush a blink dagger and start to control team fights. Or, if you're dominating and you're up in gold and kills, you can transition into something like an Armlet and crush everybody with ult + rightclicks. His ult is also invaluable against invis heroes, which you will see a lot of in low MMR games if you start playing against people.
And yeah, just to speak to your League experience a little bit, runes+masteries are one of the (many) reasons I can't stand League. I hate that it gives new players an even sharper disadvantage (as if the lack of experience relative to veterans wasn't disadvantage enough), and I really hate that it forces players to make decisions about their hero role, lane choice, and item build before the game even starts. It removes a large amount of in-game adaptability, which is one of the most exciting parts of Dota for me.