I think the bar has been raised. As science has progressed and evolved, all the "low hanging fruit" has been picked.

As an example, take Dijkstra's algorithm. It's far from the only thing that he is known for and I am by no means trying to diminish his accomplishments but how many people really tried to solve that problem before him?

I might be subject to some kind of fallacy or bias but I feel like if I'd never heard of Dijkstra and was presented with the task to find the shortest path between two nodes in a graph I could have come up with that algorithm. Maybe not in the first day but eventually at least.

It's that whole "standing on the shoulders of Giants" thing. The giants allow us to see further by learning from and building on their work, but they also picked a lot of the low hanging fruits in their career. Sure they left a lot of things undone but they probably picked out the juiciest lowest hanging fruits first and most of the ones left are either less juicy or higher up or both.

As this effect continues we end up in a situation where simply getting to the point where one can begin to push the boundaries of a specific field takes decades of learning from these giants before us, and now we're millions of people all looking for those juicy low hanging fruits while there's hardly any fruit left on the tree at all.

All that to say I think it's unfair to compare modern researchers to Einstein and similar giants. Making a revolutionary discovery like these men have done is possibly less a matter of raw intelligence and more a matter of circumstance. You need the right people in the right place with the right people around them and the funding for it and so on.