This is largely an issue of apostolic succession; regardless of the theology of the communities about ordination and the eucharist (which do differ critically), the sacraments cannot be valid because they are valid, in Catholic doctrine, only when performed by a validly ordained bishop (ordination) or consecrated by a validly ordained priest (Eucharist); the absence of episcopal apostolic succession (or, in much of protestantism, even the episcopal office) means that there are no validly ordained bishops and priests around. Now that is intimately tied to the doctrine around ordination, but even if the doctrine around the substance of the sacrament of the eucharist were identical, the absence of a valid minister of the sacrament would be critical.
> Whereas, non-Trinitarian Christians, the Catholic Church views their beliefs to directly touch on what the sacrament of baptism is about, so their non-Trinitarianism invalidates their baptisms from the Catholic viewpoint.
Well, there's two issues there. Sure, it's debatable whether a non-Trinitarian would have the requisite intent to validly (if, necessarily, illicitly) perform a baptism in the eyes of the Catholic Church, but what is more certainly fatal of most baptism by non-Trinitarians would be the failure to baptise using a Trinitarian formula, which is required for the sacrament to be valid, whether or not it is licit.
> This is largely an issue of apostolic succession
There are two different cases here. Protestants differ in their ecclesiology; some retain belief in episcopal apostolic succession, others reject it. Of course, those Protestants who reject episcopal apostolic succession, there are (from the Catholic viewpoint) no valid bishops, and hence no valid priests, and hence no valid Eucharist. On the other hand, the Anglicans, and some (but not all) of the Lutheran churches, claim to have bishops with valid apostolic succession. In the case of the Anglicans, the Catholic Church has decided that their eucharistic theology is so different that their episcopal consecrations and ordinations are invalid as a result (Apostolicae curae, 1896). Presumably, the same judgement would apply to other Protestant denominations claiming episcopal apostolic succession also.
So, from the viewpoint of traditional Catholic theology, Protestants are heretics, but their beliefs about baptism are close enough to the Catholic belief that their heresy doesn't invalidate their baptisms. (Different story for ordination and the eucharist, since Protestant theology on those topics is further away from Catholic theology.) Whereas, non-Trinitarian Christians, the Catholic Church views their beliefs to directly touch on what the sacrament of baptism is about, so their non-Trinitarianism invalidates their baptisms from the Catholic viewpoint.