In some of our extensions we use backend suitelets rather than ss services. Yesterday when the NS application went down we started getting errors on the site whereas status.netsuite.com showed SuiteCommerce had no issues

Hard to say because it depends on what wrong with the NS application. But generally speaking, no. This isn't really something you should consider.

you mean avoid using suitelet?

No, I mean that making an architectural decision such as this based on the rare occasions that we have an outage is not really something you should consider. I also don't know the specifics of what happened, and it's entirely possible that there will be scenarios where your design choices are irrelevant because of the underlying service is unavailable