The pre 1966 Punjab comprised not some parts of Himachal Pradesh, but the whole state.Shimla (now capital of H.P) was once also the captial of Punjab during the British India era.

Haryana was carved out of Punjab in 1966 and Himachal Pradesh in 1971.

Abohar and Fazilka were to be transferred to Haryana as per the Rajiv-Longowal accord, which Punjab held back, and in counter effect to this, Chandigarh was held back by Haryana and was disputed upon, which finally resulted in Chandigarh to be declared as a union territory and a shared capital of both the states.This is why there is a Punjab and Haryana High Court in Chandigarh than separate high courts.

To answer your question that whether the Punjabi suba initiative worked in favor of or against Punjab, then I would say the division of Punjab and Haryana did give an identity to the people of two different language speaking groups but I do not see it as a hindrance upon Punjab's growth and potential.

Haryana has grown and developed much ahead of Punjab and is still going up the scale.
The state has a very high rate of FDI (Foreign Direct Investment) compared to Punjab probably because the state has offered a better infrastructure and tax policies in order to attract multi national enterprises to set up.

You can also see the difference in the HUDA and PUDA townships, for this you can compare Panchkula and Mohali, and see for yourself the performance of both the states in terms of the residential infrastructures.

The hilly state of Himchal Pradesh has also attracted a lot more industrial investments in the manufacturing sector, and is doing well keeping a fine balance with its natural vegetation and beauty that the state is known for.

A shared capital is not really an issue for Punjab's prosperity, because Haryana has done really well being in the same position and scenario.

Apart from the economic growth, in terms of sports and health Punjab has gone down really fast compared to the opposite graph movement of Haryana in the same categories.All the best sportsmen coming on national and international level are mainly coming from Haryana, cancer affected patients are highest recorded in Punjab in the country, highest drug abuse is also taking place in Punjab.

Overall the moral, health and fitness of the youth of Punjab has tremendously gone down and are no longer fit for national or international sports and also defence.

Agriculture sector is also tremendously affected in Punjab and the lands are no longer fertile for agriculture due to excessive use of fertilizers from the green revolution era (the peak time of Punjab in the industrial era of independent India) till now.This excessive use of fertilizers and chemicals is the the only reason for the alarming rates of cancer cases going up in Punjab as the agricultural product is all affected by the chemicals and has also greatly affected the ground water levels in the agricultural areas where farmers directly consume the water through bore wells and the same water is also used for irrigation.

It would take atleast 50 years for the soil to regain its fertility if just left alone and let the nature take place its natural cycle.

All in all, it is the people's mindset and the government which leads to a better place to live in.
All that Punjab is left with now is the music industry which too needs a good leadership, apart from this the state is left with nothing to brag about.What will happen in the coming 7-10 years is frightening.People are ready to leave Punjab at any cost.

It appears to be a finished land in making.

Both the users have made interesting statements and seems to be accurate.

Trading with neighbouring countries may sound like an opportunity but there are risks associated with it. Government may forsee the growth but you cannot overlook the problems that can arise. Punjab as a region has isolated by the Government. Instead of providing education which should be their priority, they are pushing the youth into narcotics. You can only hope for now with the new Prime Minister in action.