I remember on this very forum they were quite a few Pakistanis who bragged that India was locked from Central Asian countries, this was when Pakistan had a good influence on Afghanistan. In fact, the word used was "beg".."India will beg for access to the CPEC and Pakistan will dictate its terms or completely block India" was the tone back then.
Chabahar has effectively removed that argument. India now has a safer, better and more friendlier access. Volume of trade at the moment does not matter, neither will how effectively we use it, but being such a big market, we can now dictate what route our imports should take- a super huge loss for CPEC! which otherwise, if Pakistan was smart, could route directly through it's land. Chabahar's and Gwadar's volume of trade is not relevant to India. However, India can rally its friends to some extent against Gwadar.
CPEC has the following potential problems:
1) Security: Yes. Pakistan's security is largely improved but the world lacks that confidence. Hence, security of the goods needs to be high which is an added burden to Pakistan since it is entirely it's responsibility. Add that cost to the loan payment, transit fee may not be enough to sustain the cost incurred.
2) China: China has played it super smart. It can also decide not to use CPEC for some goods meaning it does not get affected even if it decided not to use CPEC. It in fact will continue to get returns for all the investment it has made. Pakistan shot itself in the foot by giving all tenders to CHINA. No global or local competitive bidding for tenders was ever done.
3) FDI: CPEC looks great on paper. It should have had gathered tremendous business interest but look at the FDI in Pakistan, other than China and maybe two more countries, the rest of the world is pulling out of Pakistan. An indicator that obviously can change but is not confidence inspiring considering work on CPEC is going on at brisk pace.
4) Pakistan's Foreign Affairs: India has been successful in making a lot of good friends that have started to cause uneasiness for both Pakistan and China. Throw USA in the mix and Pakistan's incompetent Foreign office, a crack is being formed that can propagate briskly to damage CPEC's real potential.
5) Focus: Pakistan's primary focus should have and needs to be to bring business into its country, something it has continuously failed to do in spite of having a promising project like CPEC.
6) India: Enmity aside, if Pakistan wants to grow rapidly as an economic giant, it cannot ignore India. China will not ignore India! If Pakistan could have taken India into confidence and extended CPEC into India, the chances of success would have been greater.
Lastly,
Pakistan's lack of foresight, strong emotions, corruption, weak leadership will be the only reasons if CPEC would fail to live up to its expectations.