N64 is a different generation to both GBA and XB360, so you’re not counteracting my core point which is “platform exclusivity wasn’t a thing so much as it was the default position.” The consoles were all too different from each other to start from a cross-platform position. Ports took a lot of additional work, thus the reason they usually happened after success.
GBA was released during that generation, you might as well say XBox wasn't in the same generation because its release date was different than the Playstations.
You can say it and I'll defend your right to say whatever nonsense you want. But it doesn't refute jack.
But if you're really fussed about it, pick one of the other myriad examples. Tony Hawk, SC64, etc.
To be fair, Banjo-Kazooie on the GBA is effectively a completely different game. It bears only a passing resemblance to the N64 games, and is 2-D. The 360 port came ten years later, and the significant effort needed to do so was justified by the game's proven appeal.
Yeah ports existed but they were far more rare then, because as OP said, it required devs to build an entire game engine from scratch for each platform. After the early 2000s, projects like Unreal engine and Unity engine started to take over game development and allow for lightweight porting efforts across all game consoles and PC.
N64 had very few ports and vice versa with the PS1. PS1 had a catalog of over 1000 games but N64 had somewhere around 300, with Nintendo franchises probably forming about 20-25% of the total catalog.
This was also partly because games engineered and designed for the N64's strengths were not suitable for PS1 and vice versa. Porting Resident Evil 2 to the N64 took heroic efforts by Capcom to compress the game into a size suitable for cartridge, for example, and even then they had to create a custom cartridge design for it. StarCraft 64 was clearly quite different gameplay-wise from its PC counterpart as a result of a lack of mouse and keyboard, which are especially important for RTS. It also required a 4MB (RAM) expansion pack to be installed onto the N64 in order to play the full game. Other differences included a lack of voice acting in campaigns as a result of cartridge size limitations.
Ports existed in the SNES and Genesis era (NBA Jam, Mortal Kombat, Street Fighter, Earthworm Jim, etc come to mind). I would argue they were far more common then as the two consoles were not far off in specs and 2D game engines were already mature by then.