Dear Terenzio, - this is how one speaks naturally, also because we are abundantly off-topic from what Luca proposed but, as they say, discussions are like cherries, one leads to another - you yourself, albeit indirectly, admit that a Mass that exceeds the canonical 45 minutes becomes a bit excessive for those following it.
And this was also true in our Bach's time.
As you well know, the Mass in B minor was begun in 1733, when the composer wrote the Kyrie and the Gloria, dedicating them to the rites for the election of the Elector of Saxony, Frederick Augustus II, to the throne of Poland under the name Augustus III. On that occasion, and in that reduced form, it was performed in Dresden on April 21, 1733.
Only later did Bach compose the other parts: Credo, Sanctus, and Agnus Dei, finishing it in 1740.
In reality, there is no news at all of its performance in its entirety during Bach's time, and this, probably precisely because of its vast dimensions.
As for the Protestantism and Catholicism of this Mass, allow me to remind you that in composing it, Bach had well in mind, on one hand, the Flemish masses and, on the other, those of Palestrina which he had partially copied, and finally, Gregorian themes.
The composer's intention was to compose a mass that was both Protestant and Catholic at the same time. That it would have the objective grandeur of the Roman school and the subjective Protestant mysticism.
The specialists say that from this point of view, it is not quite successful... but, to me (us?) it doesn't matter at all: what counts is the general result after all. No?
But let us return to Beethoven's Missa Solemnis. What makes this Mass more suitable for concert halls is not only, from my point of view naturally, the fact that it is not liturgical since it does not faithfully follow the Roman Missal and therefore cannot be performed during the liturgies of the Catholic Church - as you rightly state - but its symphonic character.
And in this, Beethoven had a predecessor in his teacher Haydn. In the final years of Haydn's compositions, being free from church patrons but referring exclusively to Prince Nikolaus Esterházy, he produced six masses that have all remained in the repertoire but which, although strictly respectful of the liturgical service, are not at all suitable for performance during it due to their symphonic content.
The influence that the Missa solemnis had on all "sacred" music posthumously was immediate. Schubert, in his Mass in B-flat major D 950, composed in mid-1828, adapted the text to the music - and not vice versa as was done before Beethoven - favoring the composer's emotional and spiritual values and absolutely neglecting the practical necessities of the sacred ceremony.
And then... one arrives at Schumann, Brahms...! But those are all different stories that would not even be imaginable if Beethoven's Missa Solemnis had not existed first.