Why should T20I be scrapped ?
Indian players you mentioned Rahul has been discarded for time being because he has been flopping, similarly Jadeja especially in batting, whilst Bumrah and Kohli have been rested. I don not think Shami is played much in T20s, and I think Kuldeep is in the squad. The squad consists significantly of regular international players, many of these will also play world cup. So a strong team fielded by India as well as NZ.
Most teams try out some upcoming players and that includes Pakistan we have tried Shinwari, Nawaz, Imad, Asif Ali, Farhan, Rizwan and many others no test playing players. This is what is exciting about it young and upcoming talent get to showcase their skills and get international exposure.
I enjoy the T20I and tests more than ODIs, which are real bore most of the time. I am not big fan of franchise cricket though as there is no loyalty for any team for me, as it consists of random international and domestic players that may have no link for the region they represent.
I am not saying scrap T20I, rather asking to put some meaning in it. The WC idea is mine - which should help raise money for ICC and distribute it relative evenly among members; otherwise some Boards are incompetent enough to cash only from T20I and destroy cricket.
Regarding the player rotation, being PAK fan it touches you more understandably - PAK's T20I ranking is getting badly exposed here. No, it's not about younger player or senior player - IT'S ABOUT playing your possible best XI. Today, SAF is playing 30 years old Junior Dala, resting 24 years old Rabada - probably you got the clue. Also, main Indian bowlers don't play much T20s not because they are not good at, rather they are kept fresh of other formats & IPL - Kohli has played probably less than 50% of India's T20Is, probably not that he is poor is the reason and had Sharma not been deputy, he would have been also poor in T20I by that logic - i.e. not good enough to play every T20I. Kuldeep is not in this series because IND decided to keep his secret intact. Amair has carried drinks in 1st 2 T20s (& in ODIs as well) in an active series and now playing in dead rubber (& Shaeen as well

), because PAK tank didn't think Amir to be good enough, rather than resting him - otherwise he would have been sent home to rest before PSL or would have played in 2nd T20I at least.
If I tell my personal feeling regarding T20 as a whole, mods will get busy - probably the clue lies in the BPL thread. Put MMHS in search and try to find my posts there

But, this thing has to be there, and every good/bad thing has a market or requirement - so, it'll stay and should stay. But, we have to find a middle point for coexistence, and my suggestions were just to do a damage control. You get bored watching ODIs, which is again understandable - it can't be worse than spending 7 hours watching Sarfraz's team; I am extremely fond of Test cricket for it's slow burning thrills and dramas, and ODIs as well, which is extremely tactical and a mixture of skill, power and strategy.
It's Andaz apna apna - I don't criticize any T20 fan, neither back myself to be an elite for my fascination of Test cricket. Some sell milk to buy wine, some sell wine to buy milk - both are doing well as long as they are not mixing something in that milk or wine.