Having a transferable warranty on it is a good thing, as long as it’s not a Giant e+bike with any kind of warranty!
Assuming you can actually see the warranty and its clear who that warranty is with.... and I wouldn't really say Giant are particularly worse than others when it comes to e-Bikes. That is the whole if you try and fix/service it warranty is void thing is standard for the e-component.
Regardless of what anyone claims or people being lucky or having 100k subscribers the Trek Warranty is clear ...
https://www.trekbikes.com/gb/en_GB/warranty_policy/
Subsequent Ownership
Subsequent owners (second or later) are entitled to a 3-year warranty from the date of purchase from the retailer on the Trek frame and Trek fork. This does not include items such as wheels, suspension forks, drive train components etc. Proof of original purchase is required.
This Warranty Does Not Cover
....
Non-proprietary products (any other original part or component) covered by the original manufacturer’s warranty
Any products not specifically included above are omitted, but may be included in the 2012-2019 Trek Care Limited Warranty.
I'd suggest you read the whole warranty including the Bosch one if you could (but you can't unless someone can actually link to the Bosch one) and imagine taking this to court and claiming you thought it covered the motor because the wording is not explicit enough and trying to claim warranty.
