"Is considered" by whom? Or just your opinion?

As others have commented I think that the language that you've used here - "very limited quality", "little better than solving quirky problems" - to describe the work Erdős did is very unfair.

He may not have been Euler but then Euler was pretty much unique.

Maybe you could have been Claude Shannon but he already solved those things. Sometimes coming later, the low hanging fruit has already been picked.

That is very relative, coming later there is a lot more fruit to pick

True, but positioning oneself to do so involves learning more now than it did back then.

I imagine the time investment required to contribute to a mathematical specialty increases logarithmically with time (and perhaps total knowledge accumulated is the reciprocal... though that assumes specialties get more and more narrow).

> Most (not all) of Erdos work is considered of very limited quality

Are you kidding? Do you have an example of a paper that you'd say was of "very limited quality?"

No. Are YOU kidding?

Here it is the list of Erdos papers:

https://users.renyi.hu/~p_erdos/Erdos.html

Please list which papers would you put at the same level of the work of Grothendieck, Poincare, Cartan, Banach, Kolmogorov, Goedel, Schwartz, Perelman or Tao?

Wikipedia explains it better than me:

" Erdős was one of the most prolific publishers of papers in mathematical history, comparable only with Leonhard Euler; Erdős published more papers, mostly in collaboration with other mathematicians, while Euler published more pages, mostly by himself.[37] Erdős wrote around 1,525 mathematical articles in his lifetime,[38] mostly with co-authors. He strongly believed in and practiced mathematics as a social activity,[39] having 511 different collaborators in his lifetime.[40]

In his mathematical style, Erdős was much more of a "problem solver" than a "theory developer" (see "The Two Cultures of Mathematics"[41] by Timothy Gowers for an in-depth discussion of the two styles, and why problem solvers are perhaps less appreciated). Joel Spencer states that "his place in the 20th-century mathematical pantheon is a matter of some controversy because he resolutely concentrated on particular theorems and conjectures throughout his illustrious career."[42] Erdős never won the highest mathematical prize, the Fields Medal, nor did he coauthor a paper with anyone who did,[43] a pattern that extends to other prizes.[44] He did win the Wolf Prize, where his contribution is described as "for his numerous contributions to number theory, combinatorics, probability, set theory and mathematical analysis, and for personally stimulating mathematicians the world over".[45] In contrast, the works of the three winners after were recognized as "outstanding", "classic", and "profound", and the three before as "fundamental" or "seminal". "

You seem to have an extremely high standard for what isn't of "very limited quality," if one has to aspire to the level of Grothendieck, Goedel, etc.. I've just barely skimmed the first few years and found several serviceable papers -- not terrible, not great, just average stuff like people would publish today.

But, since you asked, here's one of excellent quality: https://users.renyi.hu/~p_erdos/1949-03.pdf

The original article compared Erdos to Euler. They are comparable only in sheer number of publications. Erdos was a nice and eccentric fellow and a competent mathematician who liked to solve specific problems with other colleagues . Erdos is not in the same universe of not only Euler but of any Fields medal winner. His made claim to fame is his "number", but so is Kevin Bacon's.

Who was comparing him to any Fields medal winner? You said his papers were of "very limited quality." That's what I'm saying is untrue. That isn't to say there aren't some stinkers in the mix. Anyone who publishes 1500+ papers is going to have some stinkers. But, "very limited quality" as a general assessment is way, way off the mark, IMO.

Yes, Erdos and Euler are not really comparable, but that's mostly the effect of 250 years and a lot of drugs, IMO. :P