So my first thought is why do people want to limit the Gospel to “Jesus is Lord”?
But you are correct that the Gospel has far more reaching implications for Paul and it should for us as well.

@Brian because they want to include everyone.

I’m not among those who would want to limit the gospel to be “no more than announcing ‘Jesus is Lord!’” (I actually think that everything about God and what he is doing, especially through Jesus, is ‘good news’ in the biblical and ordinary sense of the phrase), but I’d probably be among those who are starting to think “Jesus is Lord!” is much closer to the sweet spot of the gospel than I first believed or understood.
As for why, for me it doesn’t have anything to do with who is included (though I’m not sure what Taylor means there), but rather what, on the whole, the gospeling of the OT and NT seem to center on, and the intended implications of that message. The gospel of the OT tends to be a statement about who reigns, who has ultimate competence/ability/power, namely, the Lord, and what he does with his power and why. The issues of power/abilities, character, and agenda seem like the central issues in deciding who to trust and follow (and how much). Just like every election, it seems. Similarly, the gospel of Jesus was that the active and healing administration of God himself had finally (again) come near, and he demonstrated and talked about who has ultimate power and character–what the government of God (led by Jesus) could and wanted to accomplish and how. Finally, the gospel of Paul seems to center on announcing the same substance, but by focusing on (i) the person whom all this came through–Jesus as the human apex of God’s administration/reign (“the Lord”)–and (ii) the story of how this Jesus-led, God-administration rescued and continues to rescue the world (namely, his cross and resurrection). All of this is “good news” (and every detail of the story and its implications besides). And Jesus is now revealed to be at the deep heart of it. The explicit and implicit invitation of all these “gospels” of who has power and what’s being done with it is to trust and follow the One who has this power, this character, this story, this agenda for humankind. The story of his loving and powerful actions is also the story of our rescue. Trusting this king, loving him, and learning to cooperate with him (entering his active and ongoing reign, receiving his right to lead), is the obvious hoped for response to this good news (from the OT all the way through).
So the gospels of the OT, of Jesus and of Paul are very much the same in terms of substance and issues, it seems to me, but told by different people in the story and at different points within it. They are all statements and demonstrations of who in the world has the power, character and agenda for the world that can and must be trusted.