Yep, it is one of the today's world paradoxes: The less useful a novelty gadget is, the more complex the science behind its workings is...

But on the other hand very often a thing with very complex science behind is at the end very easy to make. And often vice versa is true as well...

It is indeed around that figure, but exact value depends on the arc voltage.
Because the higher power arc tend to "hold better" (less likely to extinguish), the higher power lamps are designed for higher arc voltages in order to keep the circuit current, so electrode and ballast losses and ballast cost at minimum.
This mean the multiply gets higher with higher power MVs.
On the other hand higher mains voltage at your place means there is higher voltage across the ballast and presumably you would be using higher rated voltage incandescents, it leads to somewhat higher nominal power of the incandescent as well.
I tried to better fit my model (initially I was approximating the reststance as R/Rnom = sqrt(V/Vnom); but it seems to better fit with R/Rnom = (V/Vnom)^0.43 to the published chart)

Lamp:     Ballast rating for mains voltage
MV:       120V    220V    230V    240V
50W        --     190W    196W    200W
80W        --     279W    284W    290W
125W       --     423W    429W    436W
250W       --     826W    834W    844W
400W       --    1312W   1319W   1331W

F40T12     --             147W
F20T12     71W            105W
2xF20T12   --             138W
F15T8      50W             65W
2xF15T8    --              98W
F10T8      37W             58W \
2xF10T8   (80W)            73W  > The "US" 0.21A shorter one (~34cm)
3xF10T8    --              98W /
EUF10T8    34W             49W - The 0.17A longer one (~47cm)
2xEUF10T8  --              67W - The 0.17A longer one (~47cm)

Table assumes the mains voltage and the incandescent nominal rating are the same!

tl;dr: That seems to be quite a complex effect.

So the incandescent lamp power should always be 3.2 times more than the MV lamp?

My best guess as to why is since your average person already has a FB account already and if they had to pick between making a new account and joining a forum or joining a FB group they opt for the latter. The same applies for Reddit, especially for enthusiast discussion that caters more to the 18-30 demographic. Kind of unfortunate in my opinion as forums present the information to you in a much more searchable and organized manner compared to a FB group or a subreddit. I guess FB groups and subreddits are the modern day equivalent of Yahoo groups. I remember there used to be at least a couple of them to discuss streetlighting.

What I don't understand, so much enthusiast discussion has migrated away from forums to FB, but FB is a terrible platform for enthusiast topics.
Like cars, for example. Many of the car forums I am on are basically "dead", the consensus is all of the discussion has moved over to FB. But, FB is a dumpster-fire, it's not conducive to organizing enthusiast thoughts/activities into a searchable, logical database.

The only combo that is even kinda possible is SOX18 on a F32T8 electronic instant start ballast which does work well

Unfortunately the image is too pixelated for me to really tell. Top appears to be fairly rounded so I'm thinking older GE.

If you can get a clear shot showing the slipfitter then I might be able to get a more positive ID.

The louvers in the first link are very similar to the C and M Kawartha but it's not an exact match as the Kawartha have the centre v channel extend below the body of the fixture while the ones in the link have flush v channels.

Assume:
220V mains
Standard 125W MV (so 1.15A nominal)
Ballasting lamp rated for 220V

Then the incandescent rated power should be 400W.

Real power would be:
MV: 125W
Ballast: 157W
Total: 282W