I agree with RTO.
Why a global TA can't be used is beyond me. It would be far easier to have a standardised TA of FL180 rather than having to fumble around with all of these different TAs for different countries or areas.
The transition altitude and level is tied in with the local terrain.
Why have a TA of 18,000' in a country with low terrain? In somewhere like Australia there is not much in the way of hills to hit so isn't it best to have as many aircraft as possible flying on 1013 so they don't have to change QNH all the time throughout flight? On the other hand a country like the USA needs a high transition altitude because they have much higher terrain and you don't want pilots getting caught out flying on 1013 when the QNH is 885 and losing terrain separation. A LSALT is not very meaningful if it is expressed as a Flight Level!