The thing about Pyke is that he is high risk high reward. Playing passively on Pyke automatically puts him behind. He can't farm efficiently as a solo laner and he just doesn't farm as a support. That means he has one avenue to get income to supply an assassin build (which is more expensive than a traditional support build); Kill the enemy. If he can't get gold, then he can't get ANY gold besides passive generation, which is miniscule or through traditional support means of assists, which provide little gold compared to the budget needed for assassin's.
Pykes abilities are all laid out for the enemy to see. That is to say, there will always be a warning before the actual effect takes place. His hook has a charge and takes time to travel. His stun is easily trackable and places him RIGHT next to the enemy unless the Pyke does something fancy or is escaping. If the Pyke is escaping, then that means he isn't getting gold, putting him further behind. His invisibility gives both a visual and an audio warning before he can get into range of any ability. His ultimate places an X on the ground, which is not easy to hit with an awkward delay for the Pyke player to try and adjust to.
His hook does not go through minions. His stun puts him into the enemy if used aggressively. His invisibility has a detection circle and plays a specific audio sound if you are within the ultimate execute threshold. His ultimate can be healed or mobilitied out of. His ultimate places him wherever the enemy was hit, even if they weren't executed, which means he places himself in the middle of the enemy if he didn't kill them AND doesn't get any gold, which is his major gold income generator.
Now, the passive. It only works when he breakers enemy vision, which means he will never regenerate the health he took from ONLY champion damage that CAPS after a certain grey health amount is reached. As long as Pyke is actively engaging with the enemy, he will not be regenerating that health back, which is also not a stat he can artificially obtain.
His damage, you say? If you check the graphs at the end of the game, even an ahead Pyke rarely scores in the highest damage dealers of the game. He might break even with his other teamates, but that is one heavily ahead Pyke, which probably means he was exceptionally good and/or you made enough mistakes for him to deal that much damage. A Pyke can only 100-0 an enemy if he is dueling one person in the mid to late game after having a successful early game. Otherwise, an external source must help him break that threshold for his ultimate to become an execute, which could still miss.
There you go. A thorough breakdown of what Pyke does, which should lead to understanding how to counter him. You don't poke him, you poke his ADC. If Pyke wants to go for an all-in, then the ADC is an easy kill and all of a sudden he is stuck between you, your laning partner, and your turret. An aggressive Pyke is a more exposed Pyke. Vision control hurts him more than any other champion in the game. Poking him still works if you can damage him more than his passive will heal, so strong, persistent poke is exceptionally strong against him. Yes, you won't kill him through it, but since he is an engaging melee assassin, he won't be able to do what his design is built for. That means he will be running away and thus not having a sufficient gold income to support the power he'd need to be a viable damage threat.
As with all champions, he has strengths and weaknesses. Optimal play and counterplay. Great decisions and extremely bad decisions. It all resides in game knowledge, controlling what you can, and the skill level of your opponent. If you play into a good Pyke and/or provide multiple instances of being hooked, stunned, and in general being "pick-able", then yes. He will get ahead, as any champion would if you played into their strength.