Wrong.....nope: Right!
You have quoted from an encyclical of Pius XII, where he is suggesting that congregational singing would be a good thing. This is not a legislative document on the mass. Such singing was not required - and certainly not by what Pius said in your quote.
In terms of time, Pius was the last of the old popes - the one of the Tridentine mass. So regardless of what resulted on diocesan or parish levels from his writing (which in fact was very little), it was anything but a long established, and widely followed tradition. There were however local variations in the use and extent of music in low masses. From place to place.
So, I will repeat my statement, as it is correct in light of mystical spirituality, and of the writing and reflections of many saints, beati and scholars:
"The mass is better without music, as then one must concentrate wholly and completely upon the mystical sacrifice and all too real miracle taking place in front of you, under the appearance of bread and wine."
The person who wrote those words - myself - is one who has had much study and training in the field of Sacred Music. So I think I know whereof I speak.
You said the Mass was better without music - Pius says that:
A congregation that is devoutly present at the sacrifice, in which our Savior together with His children redeemed with His sacred blood sings the nuptial hymn of His immense love, cannot keep silent, for "song befits the lover" and, as the ancient saying has it, "he who sings well prays twice."
And if you want some saints and scholars, here are two:
Hence the use of music in the divine praises is a salutary institution, that the souls of the faint-hearted may be the more incited to devotion. Wherefore Augustine say (Confess. x, 33): "I am inclined to approve of the usage of singing in the church, that so by the delight of the ears the faint-hearted may rise to the feeling of devotion": and he says of himself (Confess. ix, 6): "I wept in Thy hymns and canticles, touched to the quick by the voices of Thy sweet-attuned Church." (ST II-II q. 91 a. 2)