Talk about wild speculations/generalizations.
alpha, such large speculations don't constitute a credible argument - not even close. You could just as well say ~'if Jesus would not have been crucified, then - insert whatever you want'.
Even so, let's address these speculations:
Nobody gave modern liberal democracies their knowledge and freedom. The philosophy and societal structure that enabled them (and the thinkers/scientists that built their bases) to make these advances is also the one that lead to their system of governance.
If you give Rome modern science and technology (and the time, means and will to understand it) and economic knowledge (which it almost completely lacked) then it would not be Rome any longer - not in the least.
And even so, it would not be competitive in the modern world - slave societies are not conductive to innovation on the scale of free societies (not even close), nor are they economically as efficient (by a large margin - you need a LOT of highly trained labor - not slaves; also, slaves can't pay for their consumption, they don't contribute to the economic circle). War is not economically efficient efficient with a modern economy (as opposed to what the romans had, when it was highly efficient for gaining wealth), etc.
Notice the changes made in Japan's social structure in order to become competitive (hint - they went far beyond learning technology). Notice its system of governance and values today - an all but inevitable result of the changes it made in order to become competitive.
You make the mistake of assuming that 'sophisticated', overpolished rituals equal advancement.
The one area you can made the case that romans were advanced was their law; and the one area japanese were advanced was hygiene.
As for the rest, proud warrior societies or elaborate court etiquette are a dime a dozen; not that hard to develop the mind-set (as history repeatedly proved), and at most of transitory benefit (in wealth, freedom of people - as opposed to a small oligarchy -, other actually objective criteria for measuring advancement).
O, and modern liberal democracies ARE the most prosperous, the freest states in history. THAT'S A FACT.
Feel free to look up history books and come with counterexamples - that don't include hugely extravagant/uncertain speculations: ~'if you gave them this and that they would have been etc'.
You see, then I could just as well say - if ET would come tomorrow and give liberal democracies the secret to universal freedom and abundance, they would still be wealthier and freer.