Well, the problem is it won't draw it like you did, it'll draw it like this:
I'm looking down the line, and it might be feasible to swap Caste System and Protected Trade (and the techs after them in the tech tree of course) so that we can group the two Great Houses 'derivative' techs together and beat this issue.
It is far from optimal, but might not be too bad, if (and only if) you could still include the requirement icon on the tech label (as gets done with non-linked AND requirements).
While I'd be very cautious using this much, I'm looking at doing this for Law of Arrakis(let's call it LoA for the moment), as I'd like it to be reachable from any of Divine Mandate, Feudalism, or Great Houses, but you can't draw lines from all three. It's too important of a tech for expansion to be hitched to only Feudalism or Great Houses, it should be reachable from either to keep them roughly equally viable options (where the decision is based on your strategic plan). If for instance it had OR techs for Divine Mandate OR Great Houses only, It would make Great Houses somewhat better than Feudalism just because it leads to LoA.
To be clear; you get a 20% research cost reduction for a tech that is an OR requirement for a tech you already possess? Am I interpreting that right? So if A or B are needed for C and I want them all, then it is cheaper for me to go A-C-B than A-B-C?
Embarrassingly, I didn't actually know that.
I think you got your letters backwards, but yes, for every OR tech you have, you get an additional 20% research mod (I'll come to that) towards that tech.
Research mods are something not shown in the interface, so most players are blissfully ignorant of how they work or when they are working for you, but it's also one of those things that shouldn't be explicitly shown as it breaks immersion a little bit and would encourage a more min/max play style. For the average player it's enough to know that having additional ORs does make it quicker to research (I've known this principle for what seems like forever as I know RevDCM at least has help text when hovering over a tech saying it speeds up another, is that in DuneWars?).
For the sake of balancing though, it's good to know the mechanics. A research mod does NOT affect the COST of a tech, instead it's a multiplier to a player's current research/turn. So if you are producing 100 research, a +20% research mod means you actually apply 120 research to the current tech that turn. So a tech with a cost of 5000 takes 50 turns @ 100 research per turn, but 41.6667 turns with a +20% research mod. That's where the cost reduction to keep them equal required above comes from:
1.0 - (41.6667 / 50 = 0.8333) = .166667
OR
16.6667%
Tech Diffusion also acts on a player's research modifier, adding to it based on how many players they know that have the tech already (with a bonus if that player has open borders) and how far behind they are in techs compared to the tech leader.
Now, the BetterAI merge gives us a GlobalDefines setting that differentiates between the first OR tech and each additional OR tech. This means we can set the first OR tech to not give a research mod bonus, but at present it's set to 20% for the first and for each additional, and I've avoided changing that as it affects the research balance considerably from what we are used to seeing since almost all techs have at least one OR prereq. It would in effect slow down tech progression.
But it is rather illogical that setting one OR tech makes a tech cheaper than giving it an AND tech. The mechanic
should work in principle to encourage you to seek
additional ORs before researching an expensive tech if you can put it off, but giving a bonus for the first OR doesn't make a lot of sense, nor do players realize at all that that's happening. The good news is that despite the fact that it's illogical, it's a hidden mechanic that doesn't really break anything, so it's not really imperative that we change it either.