I think it's important to realize that such a policy is not a definitive statement about whether or not another group has "valid sacraments". It isn't like the legalistic western position where if a certain formula and requirements are met, it 'worked', and if not, it didn't.
There is only one Baptism, not many, and that Baptism is into the one church of God. Whether or not God has accepted the Baptism of those cut of from the one Church to various degrees, we do not know. The Baptism of one coming from another Christian group, especially the more traditional ones, isn't a second Baptism, it is the person's Baptism. However, that is not to make a definitive statement that the person was not previously a Christian, and was previously unbaptised. It is a completion of whatever was lacking before.
In the Case of the Eastern Orthodox Church, the fact that there is no Baptism is a testament to the view of the EO Church as Orthodox, though separate. I think Fr. Peter has some articles about how that is the historic treatment, not some modern ecumenical tendency.
In the Case of Eastern Catholics, in many ways they are like Eastern Orthodox who have chosen to commune with Rome. If you look at the Coptic Catholic Church, which is probably central to Coptic Orthodox policy, it was only a century or two ago that a small group of Coptic Orthodox broke of from the Coptic Orthodox Church and entered communion with Rome. Would such an action remove their ability to Baptise?
The policy of the Church today is very clearly that Eastern Orthodox and Eastern Catholics, who have been baptised by priests, in the Name of the Father and the Son and the Holy Spirit, by tripple immersion, are received by Chrismation. Others by Baptism and Chrismation. (In this case it is even debatable whether it is correct to say that they are received by Chrismation, or whether they are in fact received by confession, and the sealing with the myroun is repeated, not as a repetition of the Baptism and Chrismation, but as a sign of the renewal that has taken place through reconciliation).
Even regarding those two as separate Sacraments is something borrowed fairly recently from Catholicism. The synaxarium records an interesting event: a woman baptised her children during a storm at sea when she feared they would not survive. They were on their way to Alexandria to baptise the children. They ended up arriving safely, but when the Patriarch tried to Baptise them, the water would become solid every time he approached with the children, and would liquify again as he withdrew. He inquired about what happened, realized that they were already Baptised, and completed it with the Myroun. This is the same thing that happens today, it is seen as whatever is lacking being completed, rather than repeated. In the case of Latin rite Catholics, the immersion is lacking, so it is completed along with this chrism.
Despite the policy being clear, there may be some variety of practice. It is technically within the authority of a bishop to choose, for whatever pastoral reasons, how to receive people in his diocese, including choosing to receive Catholics by chrismation alone. It is arguable that is a more proper practice. However, for the most part, he unified decision of the Synod is maintained. I'm sure many will disagree with my interpretation of the underlying reasons, and some will be able to point to exceptions where this policy has not been followed (I even know of an EO who was received by baptism, which is clearly wrong). Clearly there is an ongoing trend away from the more conservative approach of rebaptising everyone, with increasing openness to reception of Catholics by Chrismation, and reception of EO by confession alone. However, to my knowledge, this is still the official policy of the Patriarchate, bearing in mind that the bishop has authority in his diocese, and has a great deal of latitude in acting according to the pastoral needs in his diocese..