I think people need to be reminded of why DRS was brought in.
For 2010, refuelling was banned. The 2010 Bahrain GP was one of the most pointless races ever, with no overtaking among the top ten runners except on Vettel who was having a car problem.
If you are talking about pre-DRS, you can't make comparison with races before 2010 in which refuelling was allowed, because in those days you had cars on different fuel loads which made overtaking easier. Plus you had different strategies depending on the amount of fuel people wanted to qualify with.
You could argue that DRS is no longer needed now that you have tyres which don't last the whole race, but unfortunately we have the silly tyre rules which means all the faster runners tend to be on the same tyre, with a similar amount of degradation. If we got rid of those rules and everyone could choose their tyre strategy freely, maybe we could do away with DRS and still have overtaking.