As for institutions, there are more discretionary guys than systematic.
I mention guys because:
1. The term trader is a very broad term.
2. There are a lot of quants. Most end up as analysts, some develop "grey box" models, very few can develop "black box" models.
3. All the grey-models developed are executed by trade desk clerks. They add executionary and non-quantitative values to the "grey box". Clerks call themselves traders.
4. There are dealers who uses discretion. They make markets and etc., they don't act in the same way as a clerk. Different size and fundamentals.
5. There are props in large institutions. They vary in style like the public/retail, but mostly dicretionary (uses technical analysis and a more "inside" fundamentals... 95% or so...). Usually, a systematic trader doesn't get into this category... It becomes more like "internal hedge fund" role.
Finally, the demographic of the "style" is pretty much the same as the public or retail. It's just that, you need a strong crudential behind you to actually become a "trader" for an institution, unlike retail where all you need is some capital or a bit of luck.
It's a bit obvious that the institutional traders are more sophisticated than "MOST" retail, due to the selection process. Not all though... at least you won't see all the immature questions and replies, you see in ET.
As for system trading, it becomes a bit different. Like I mention above, the quants are usually too "academic" just running numbers and sticking data inside some formula. In a sense, they are ignoring the market... maybe a better way to mention this is they are obsessed with something different.
In reverse, the system developers in retail are too immature. I've seen a lot of good ideas (thanks for posting them) which isn't applied and gone to waste. It's a matter of sophistication from knowledge and experience.
Another aspect is the competition surrounding you that gives you the drive. Eventually, we're all fighting for a larger portion of the pot. Most are proven traders or bunch of Ph.D.s... it becomes interesting if you're in it, watching money and pride all tangled up...
Oh... there's a high turnover...
