So much of life is a never-ending cat and mouse struggle
- criminals vs police
- stealth vs radar
- antibiotics vs resistance
- accountant vs tax code
- predator vs prey
- hackers vs security software
You're completely right that monoculture is a bad idea: we see the benefits of making our food a few percent cheaper, but we expose ourselves to massive risk that is rare and difficult to assess. Generally we as humans should seek to minimize these rare but catastrophic risks, but I'm not sure we have the discipline to give up the short term gains and benefits.
I don't think we're capable of that kind of discipline as a species. I don't think our society can even be structured to have that kind of discipline because we value living in the moment more than we value the long term.
Still doesn't solve the bigger issue of monoculture dominating the banana industry. The growers will shift to this type and something will come along and they're right back in the same boat they were in before, scrambling to find a new variety resistant to the new threat.