Wormholes

I lost few Ventures due to my lack of experience.
For example https://zkillboard.com/kill/55371980/
I had shitfit (useless tank, large sig). Bomber that ganked me had pre-scanned site and double scram, no way a venture can escape from that. Extra sig made large difference in damage taken per torpedo.

Venture is also 100% dead when you enter a hole camped by dictor or any sort of bubbles really.

Prospect would laugh at both of these and escape easily. Torpedoes hitting 30m sig moving at 2km/s do like 30 damage, and that's only if he manages to actually scram you, which is much harder due to 4 stabs.
With that kind of speed you will outrange him long before he kills you.
Also, bubbles and camps are just silly setbacks instead of 100% death

Add double ore hold and higher difficulty to get scanned down...

Now, from economical standpoint:

2x harvester costs 7m+
prototype cloak costs like 1m
Full ore hold of C50 gas (which is very common) costs 26m


So, fully fit gas Venture costs at least 7-8m while carrying up to 45m isk (C320).
Full fit Prospect costs ~27m, while carrying gas worth up to 90m

Your argument would be good if you applied it to something else, such as Exhumers.
Using 200m ship for mining 10m/h vs using 28m ship for mining 50m/h is huge difference.

And why avoid gank? To maximize profits, to not get frustrated because you died to first person who saw you on dscan.
I fing actively avoiding ganks much more fun than undocking venture after venture just to die