I believe this statement contradicts itself. Tradition indeed has nothing BUT *edit* scaling *edit* benefits, with the value of those depending on it's fit to strategy.
*edit* In retrospect this is not correct, legalism does not truly scale, and is more of a 'bootstrap' sp
LE, which you mention, is the most powerful and obvious of these. Any percentage gain of any resource is scaling, and 2+ 15% is most definitely that.
Monarchy(?) provides 50% less unhappy in your capitol as well as money per pop point. It scales very well, just forces you to get the gain out of only one city and force growth there.
Liberty I have much less experience with, I think of it more in terms of bootstrapping your empire growth than efficiency. It's harder to break its results into a numbers game!
I don't want this to become a huge argument and whatnot but talking about generic opening policies involves neighter oligarchy or 20% to wonder policy. Each of those are insanely situationnal and disregarded for competitive play. Oligarchy is more of a MP defense/post .275 adaptation to improve a players' learning curve for the time being.
Back to LE/Monarchy.
LE is really the central piece of tradition. It is the main reason why tradition is competitive with liberty in most openers/strategies. It simply involves playing sightly differently like build order etc.
The 15%, even though it scales, only applies to the growth food. That is to the exceeding food used to grow the city. Because of that, it is usually a marginal gain all game along. Chances are, even after getting hospital in the late game and having every maritime CSs availible allied, that your capital will get maybe 4-5 extra food for growth through this. In the early game, it's almost never more than one extra food. Thus even though this part of the policy scales, the true strength of LE is in the +2 food in all cities. This significantly speeds up the growth in super small cities for expansive play and allows to work two lumbermills for free, increasing the production once you wish your cities not to grow anymore. In fact, even if you only have your capital, this can cover for a settled meritocracy GE production-wise and provide an extra 1gpt if both forests are riverside.
My comments with regards to the lack of scaling was more that once your cities are really tall, it's net effect is almost negligeable, thus it doesn't scale well in that way. On the other hand, it scales decent with expansion in the same way that 50% settler cost and 25% worker speed does. So both are solid in early game but slowly useless as the game goes on "aka my definition of lack of scaling" lies in that the policy becomes worse and worse as the game flies as opposed to keeping a similar relative potency.
Great examples of scaling policies would be theocracy/scholasticism/the +1 beaker/TP and +2beaker/specialist in rationalism etc.
Monarchy, I have to give you, is a scaling policy. This being said, it is lackluster in the early game and generally becomes a good pick later in the game when you suffer happiness issues to keep expanding/growing/warmongering etc. as such, it is really not a good pick in a "first 3 policies" perspective opener regarding liberty vs tradition.
I guess one could argue that it gives a plus value to picking tradition over liberty since it opens up an ok late-game happiness policy with decent scaling (scales to capital but not to whole empire again making it somewhat situational)
As you mentionned, liberty is definitely more of a bootstrapping policy tree. Huge instant benefits that become nearly useless somewhat fast in the game. It is very, very hard to truely math out and it is highly strat dependant. On the other hand, it is possible to argue that most instant benefits can be obtained through tradition by simply changing build order and working tiles differently. The only true exception is the wonder rushing/tech bubbling from meritocracy that can't be played any other way and that is part of so many strategies.
*Edit* I said it somewhat late in my post so I figure I will define what I mean by "lack of scaling" regarding a policy :
A policy lacks scaling if it becomes less and less potent as the turns pass. This means, a policy may have an actual clear mathematical scaling factor and still be lacking scaling over time, thus making a policy saving option more viable over the lenght of the game.
As such, legalism would be totally lacking scaling. You can see it's benefit in two ways. Either the total amount of hammers saved or the extra benefits in culture (given you would NOT have built those culture buildings if it had not been for legalism). The first approach is a flat number that never changes. The second approach gives a lot of extra CPT at the time of taking the SP but slowly less and less in proportion of your total empire culture as the time flies. Thus making it's benefit less and less potent over time.
*edit* fixed some major typo
