Formal word for overhyped?
Solution 1:
Overhyped might strike you as informal simply because it's relatively new. The first citation in the OED is from 1979 for the verb and 1980 for the adjective. I can see how overhyped could seem like an unusual word choice to refer to something that isn't relatively modern. If you are looking for another word that's used in settings in addition to advertising and may be more appropriate, I suggest
inflated (adj.)
Elaborated or heightened by artificial or empty means
an inflated style of writing m-w
pompous; bombastic; high-flown
increased or raised beyond what is normal or valid Webster’s New World College Dictionary
Englarged beyond truth or reasonableness vocabulary.com
Technologies tend to get overhyped (inflated expectations) after their initial introduction to the market. G. Grant and R. Collins; The Value Imperative
... the desperation for a 'miracle recovery' so common in fiction or media reportage is shared by the loved ones of the patient, leading to 'costs of inflated promise', an over-hyped assurance that is further communicated and perpetuated in the press. Matthew Colbeck; The Language and Imagery of Brain Injury
...Consumers' Research Incorporated which reported on competing products' quality and value and sought particularly to prick the bubble of inflated advertising claims. M. Bevir and F. Trentmann; Critiques of Capital in Modern Britain and America
The second approach meant advertising poor quality products in a flashy manner ('hucksterism') and treating consumers as 'gullible dupes' who would be convinced by inflated product claims. Caroline Koegler; Critical Branding
Such criticisms might be seen as having a primarily anecdotal value, merely adding to the commercial overkill of a media-inflated event. Graham Huggan; The Post-Colonial Exotic: Marketing the Margins
The other conflict that will not be found in this volume is an action grandiloquently or facetiously known as “The Lowell War.” This inflated event occurred on November 21, 1857, at the town named in the title. Le Roy Barnett; Michigan's Early Military Forces
When experiments have used these methods, their findings have indicated that when advertisements that inflate the product performance of a consumer product are made, the participants reported a higher level of intent to buy the product. David Hill; Encyclopedia of Deception, vol. 2
Packaging may be cleverly designed to give an inflated impression of quality. K. Brumfitt et al.; Marketing
But I consider that the particular illustrative example used here will give the non-statistician a grossly inflated idea of the power of the moving average to give useful information. Journal of the South African Institute of Mining and Metallurgy
Both Klein's and Manzoni's oeuvres featured Conceptualism's irony. Klein's exhibition of literally invisible “paintings” (the “zones of immaterial pictorial sensitivity”) foreshadowed many Conceptual works that carried the inflated idea of the “last painting” ad absurdum. Thomas McEvilley; Capacity