Why do you say shorter block times is a very real disadvantage please?
As the time required to propagate a new block throughout the entire network becomes a greater percentage of the bock-to-block interval, the system spends a greater percentage of time in an indeterminate state. This inconsistent state provides lower security due to the differing views that payer and payee have of the state of the system. This leads to a higher percentage of unsettleable transactions.
I don't see the disadvantage in better specs...
If the specs are unquestionably 'better', then by definition there can be no disadvantage. However, Litecoin's 2.5m block interval is not objectively better than Bitcoins 10m. It is merely _different_. There is a tradeoff between time to settle and determinism of settlement.
If Litecoin's 2.5m was objectively better than Bitcoin's 10m -- merely due to the shorter block interval -- why not 1m? Why not 15s?