Morphy's games deserve to be studied, for sure. Both for his tactical brilliance, and the clarity of his ideas (very easy to learn from and understand).
He also played in the Classical/Romantic era of chess, which is a good place to study from when developing your chess foundation. Will give you good fundamentals.
I like Watson and generally appreciate his reviews. I do think, however, in the case of Tarrasch, he is somehow blind to some nuance. Yes, Tarrasch makes what seem dogmatic pronouncements. On the other hand, I have seen several instances where he undermines his own dogmatism a few pages later. It would be easy to see these instances as contradiction, but it is also possible to read them as playful irony. I rather suspect that Tarrasch's dogmatism stems from a bit of dry wit that many readers miss.
When you are teaching beginners, especially young beginners, who have a tendency to get into trouble playing bishops to squares where they might be attacked by a discovery, it is useful to be dogmatic in the insistence of knights before bishops. However, when that student then faces the Winawer variation of the French, you need another tack. I think Tarrasch understood these contingencies and that Watson largely misses it.