Why should duration be considered a measure of a constitution's success? The goal is to "provide for the common defense, promote the general welfare," etc. If it achieves this for 50 years, then is replaced by another that also succeeds for 50 years, is the result in any way worse than a constitution that lasts for 100?
I think scraping a constitution and writing a new one inevitably brings about political turmoil precisely because the stated goals aren't being accomplished.
You're right in that duration shouldn't be the only measure, but I think the longevity says something about how society feels in general about the constitution's efficacy.