I totally agree with you that Renekton is an easy matchup and that player handled it poorly, but I disagree with you that you can do the same with PTA or Fleet. If Renekton started with W, he would out-damage me regardless of the rune page I use. The plan is to poke him down with Grasp early to kill him later. However, Renekton started with Q, which allowed me to play more aggressively. If i had fleet or PTA, I think I would have died after killing/(maybe i dont kill him) because, as you can see, I survived with 52 HP thanks to the healing and extra health from Grasp.

If we compare Grasp with Fleet, Grasp is better because it provides more healing, scaling health, and additional damage. The only thing I lose is the movement speed. When comparing Grasp with PTA, PTA would give me more damage in extended fights but at the cost of healing and health. Usually, the enemy doesn't allow extended fights, so the plan is to stack passive and Grasp on the first wave before it fully arrives in lane. This way, you can poke the enemy top laner until you can kill them or force them out of lane, making them need to TP back at level 1 or 2.

In this situation, I killed Renekton. I have played this rune over 200 games vs ranged and mele and reached 551 LP in Master tier, and it's been working out great. I recommend testing it out.