Don't get me wrong, I understand your frustration however I think you are overreacting a bit.
REI has a great return policy you can simply return the bike and shop for another one.
That being said gravel bikes usually come with cx or similar motors. Since they are marketed towards gravel riding 20mph is assumed to be sufficient. Even with cx that bike is still a great bike with a unique suspension setup and in this pandemic the price is very good. Moreover 28mph is a legal issue not a quality issue. CX version of this motor is just as good of a motor as the speed version(in the previous gen many people derestricted their motors and they were just as good if not better than their speed counterparts).
If Bosch let the dealers to decide the speed limit at the time of sale(via firmware) than this would not have been a problem to begin with. Since form factor is the same, on paper switching motors should not be a problem however I don't think Bosch or Cannondale will ever be ok with this, it is too much of a headache/ labor etc.
That's not how it works. If a merchant advertises a product, they have a legal obligation to deliver the product as advertised. Consumer protection laws vary from state to state, but generally false advertising is illegal. In this case, REI continues to falsley advertise these bikes as a Class 3. Furthermore, there are actual Class 3 versions of these bikes available. It's not outside the realm of possible for REI and Cannondale to make this right by providing Class 3 bikes.
In Washington State false advertising is a misdemeanor.
False advertising.
Any person, firm, corporation or association who, with intent to sell or in any wise dispose of merchandise, securities, service, or anything offered by such person, firm, corporation or association, directly or indirectly, to the public for sale or distribution, or with intent to increase the consumption thereof, or to induce the public in any manner to enter into any obligation relating thereto, or to acquire title thereto, or an interest therein, makes, publishes, disseminates, circulates, or places before the public, or causes, directly or indirectly, to be made, published, disseminated, circulated, or placed before the public in this state, in a newspaper or other publication, or in the form of a book, notice, hand-bill, poster, bill, circular, pamphlet, or letter, or in any other way, an advertisement of any sort regarding merchandise, securities, service, or anything so offered to the public, which advertisement contains any assertion, representation or statement of fact which is untrue, deceptive or misleading,
shall be guilty of a misdemeanor: PROVIDED, That the provisions of this section shall not apply to any owner, publisher, agent, or employee of a newspaper for the publication of such advertisement published in good faith and without knowledge of the falsity thereof.