Well, it's not really exclusive, it's being developed cross platform for Wii U and Switch.
Besides which, plenty of exclusive games have framerate problems.
They shouldn't have especially when they ate developed by a first party studio. Nintendo knows the hardware for the Switch best it would suck when 9ne of the most ambitious Nintendo games would suffer from notable frame rate issues. As for Wii U well Nintendo knows the system well by now and it has been in development for that platform for quite some time.
As I wrote... "Exclusivity" is focusing on corporate ownership rather than technical issues.
In fact, it's not even Nintendo's own platform, they outsourced core HW and even API to NVIDIA.
They do not have a Cerny scenario where their software dev teams were at nexus of HW design.
Nintendo literally just picked up NVIDIA's Shield 2 platform and APIs and signed on the dotted lign.
Wii U/Switch remain very dissimilar platforms (Xbone/PS4 are more similar in CPU/GPU architecture).
And again, why in the hell does early pre-release footage mean anything?
Any game is unoptimized at this point. Multi-platform, which this is, even more so.