Not so. Ireland was a net food exporter for the duration of the famine. The problem was political and economic.
Bananas are kind of a weird case for multicropping, because they are all sterile clones. So this makes them horribly susceptible to every disease under the sun.
https://www.irishexaminer.com/opinion/columnists/arid-202289...
Do you have a better source, which you think refutes their arguments?
They are arguing that Ireland was not a net exporter of food because a large portion of Irish crop exports were oats, and oats are not food.
The supporting arguments are worse. For instance, they state that oats are usually for horses' consumption. Further, they state that the average farmer would not know how to prepare the oats for human consumption.
All this seems obviously false[1].
As a general point, the obvious point of comparison with Ireland would be the various states of 1840's germany, also heavily reliant on potatoes for sustenance. They also got the potato blight, but there was no great famine.
[1] they also give some figures, which I won't comment on.
A current example would be the ubiquitous banana. The cavendish banana (the most common variety you'd encounter in your produce isle) is under attack globally and is at risk of being wiped out. And this isn't the first time that's happened. The banana your grandparents grew up with, the Gros Michel, while not extinct is no longer commercially viable.