The keys in Jewish understanding meant protecting the scriptures. The RCC has never done that, they add fairy tales and false doctrines to it.
The keys were also for discipline. The RCC has never done that with its leaders throughout the centuries unless it suited their purposes. They hide the sin of their leaders. They ignore 1 Cor 5:11.
And Jesus shows the keys were for spreading the good news, as you say. The RCC has not done this the way Jesus and the apostles did it, they forced people to convert and maintained control through fear. Now they cave into popular demands for divorce, gay marriages etc.
The RCC misuse the keys as a means to maintain control over the masses, they do not use them as they were meant to be used and so they have false keys, like their doctrines.