…the samples are all exposed for the taking…
I’m afraid that is the whole point of this community. It’s in the terms:
Your samples may be freely used by anyone accessing the Pianobook library. Usage of samples may be to create commercial and non-commercial musical compositions or recordings, however repackaging of the samples into a commercial product will be forbidden without your express permission.
In fact it is recommended (https://www.pianobook.co.uk/submit/) that uploaders include the raw samples so that it will be easier for others to use them. Many Pianobook users count on the ability to use the raw samples in their sampler of choice.
If allowing others to use your samples however they like (other than to create a commercial product) is a problem, then this is probably not where you want to upload your sample instrument.
As for the easiest Sampler to create samples for, I would say the Decent Sampler is pretty easy though not as feature rich. Feel free to upload Halion versions of your instruments, but please do also include the raw samples.