It's not a flaw for a document to fail to be timeless.
If we could dig up the same people that created the constitution and put them in the present day, I'm sure they'd do a better job, once they got their bearings. But if you could take someone from then and drop them into today, they'd be overwhelmed and couldn't wrap their head around it.
If they redid the constitution today, I think the 2nd amendment would be worded MUCH differently. Forming a militia and being wary of your government made sense when it was musket vs musket. When a trained soldier could be matched up against an 8 year old who could shoot a squirrel between the eyes from 50 yards.
But the founding fathers would look at our country's arsenal of space lasers, floating airport cities, and hell, 1 apache helicopter and they'd focus on bearing arms for home defense REAL quick.
Imagine New Mexico being the most populace state. Imagine Manhattan, KS being the largest city. They just couldn't have forecasted the radical growth and differences of today.
Why did we stop amending the constitution in the first place? Wasn't it Jefferson who said we should take a long look at things and make changes every 20 years? We haven't had an amendment in over 240 years! What has happened is that in not making any changes to it makes people consider it a perfect document. It isn't. No document is.
When you don't make changes, it becomes stagnant and does not evolve with the times. And that's how you get people claiming their semi-automatic guns that aren't for hunting nor home defense having the constitution on their side. It's silly.