No, most of the landlords were of British descent. The rest were under control of the crown and the crown got their taxes. The upper classes, mainly British and some Irish systematically bled the vast majority of the people.

>As they would have seen it, stopping the export of food stuffs would have caused economic collapse.

They knew very well that it would have caused economic collapse only for the people in power who were at no risk of dying. And they knew very well what they could do to save the lives of people they saw starving all around them. To say they could do nothing because 'it's the system' is ridiculous. The people with power were the system. The people who starved had no real representation and that's they way it was designed by the people in power, namely the landlords and the government.

Even before the famine the reason a lot of the tenant farmers emigrated was because if they managed to be in any way extra productive and make some profit for themselves it was immediately taken from them in the form of some tax (see for example the 'window' tax). This was systematic and the people in power were responsible.