TL;DR: the relationship between <the amount of uploads per user> and their share of the total collection of files on Commons seems to follow an inverse logarithmic trajectory.
There are a huge amount of uploaders with few uploads, but their share is minimal compared to the contributions of a very small amount of extremely prolific uploaders.
This is a trend that is obvious between all uploads in general, non-bot uploads (though less extreme) and deletions (even less extreme)
Read on for a more detailed breakdown.

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On a total of 103,217,848 uploads, by 1,790,892 users, here's a quick overview of the distribution:

There are 934,991 users (±52% of uploaders) with a single upload. Those 934,991 uploaded files are ±1% of the total amount of uploads.
Counting all files from uploaders with 30 or less edits (95% of uploaders), we reach ±5% of the total amount of uploads.
10% of all uploads are reached with all files from uploaders with ±275 uploads or less (99% of uploaders)
25% of all uploads are reached with all files from uploaders with ±5,000 uploads or less (99.9% of uploaders)
50% of all uploads are reached with all files from uploaders with ±65,000 uploads or less (99.99% of uploaders)
The other 50% of all uploads come from the remaining 125 users.

(query for source data: https://quarry.wmcloud.org/query/80222)

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Same exercise, but without users marked as "bots":

On a total of 84,818,309 uploads, by 1,790,697 (non bot) users, here's a quick overview of the distribution:

There are 934,887 users (±52% of uploaders) with a single upload. Those 934,887 uploaded files are ±1% of the total amount of uploads.
Counting all files from uploaders with 17 or less edits (93% of uploaders), we reach ±5% of the total amount of uploads.
10% of all uploads are reached with all files from uploaders with ±150 uploads or less (98.5% of uploaders)
25% of all uploads are reached with all files from uploaders with ±2,700 uploads or less (99.8% of uploaders)
50% of all uploads are reached with all files from uploaders with ±28,000 uploads or less (99.98% of uploaders)
The other 50% of all uploads come from the remaining 358 users.

(query for source data: https://quarry.wmcloud.org/query/80285)

While bots account for a massive share of the data (where only a few users account for the majority of uploads), the same pattern holds true (albeit slightly less dramatic) if we exclude them.

Top 10 most prolific non-bot users:

• https://commons.wikimedia.org/wiki/User:F%C3%A6
• https://commons.wikimedia.org/wiki/User:Askeuhd
• https://commons.wikimedia.org/wiki/User:Panoramio_upload_bot
• https://commons.wikimedia.org/wiki/User:Mr.Nostalgic
• https://commons.wikimedia.org/wiki/User:Ser_Amantio_di_Nicolao
• https://commons.wikimedia.org/wiki/User:Judgefloro
• https://commons.wikimedia.org/wiki/User:File_Upload_Bot_(Magnus_Manske)
• https://commons.wikimedia.org/wiki/User:Tm
• https://commons.wikimedia.org/wiki/User:Jeuwre
• https://commons.wikimedia.org/wiki/User:Polona_Upload

You'll notice that at least some of them are actually still bots (they just haven't been marked with that role), or otherwise representative of massive archives being uploaded (likely automated)

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Same exercise, but without deletions:

On a total of 6,175,655 deletions, by 1,300,629 users, here's a quick overview of the distribution:

There are 753,843 users (±58% of uploaders-with-a-deleted-file) with a single deleted file. Those 753,843 deletions are ±12% of the total amount of deletions.
25% of all deletions are reached with all files from uploaders with ±3 deletions or less (81% of uploaders with a deleted file)
50% of all deletions are reached with all files from uploaders with ±21 deletions or less (97.6% of uploaders with a deleted file)
The other 50% of all deletions come from the remaining 814 users.

(query for source data: https://quarry.wmcloud.org/query/80288)