What is an adjective for somone who displays ‘fake’ gravitas?

Words like insincere, over-earnest, do not do justice to the type of word I need. Example sentence: The president of the company read his well crafted speech but it fell flat because of his obvious “———“.

Pretentious is the first word that grabs me. (Please use the noun form, pretentiousness, to fill in the blank. )

attempting to impress by affecting greater importance, talent, culture, etc., than is actually possessed.

Synonyms include:

affected, ostentatious, showy; overambitious, pompous, artificial, inflated, overblown, high-sounding, flowery, grandiose, elaborate, extravagant, flamboyant, ornate, grandiloquent, magniloquent, sophomoric;

Will pomposity fit?

pompous
adj. 1. Characterized by excessive self-esteem or exaggerated dignity; pretentious: pompous officials who enjoy giving orders.
American Heritage Dictionary

pomposity
n, pl -ties
1. vain or ostentatious display of dignity or importance
Collins English Dictionary

pompous
1.Affectedly grand, solemn, or self-important.
Oxford Living Dictionary

pompous
1 : excessively elevated or ornate pompous rhetoric
2 : having or exhibiting self-importance : arrogant
"a pompous politician"
Merriam-Webster Dictionary

Not sure whether this word fits your intention of "gravitas", but it does mean possible affectation with the definitions containing descriptive words such as "pretentious" and "ostentatious".

The president of the company read his well crafted speech but it fell flat because of his obvious "pomposity".

Some possibilities:

affected
affected behavior is not natural but is done to impress other people
                                               His affected manner annoyed her.

bombastic
marked by or given to speech or writing that is given exaggerated importance by artificial or empty means : marked by or given to bombast (pretentious inflated speech or writing )
                                               the bombastic pronouncements of so many politicians

portentous
trying to seem very serious and important, in order to impress people

flatulent
pompously or portentously overblown

This would best fit as a description of the speech itself, but my (former) favorite word might meet your needs:

Grandiloquence

Noun: a lofty, extravagantly colorful, pompous, or bombastic style, manner, or quality especially in language

The president of the company read his well crafted speech but it fell flat because of his obvious delusions of grandeur.

to give sufficient levity to the negative ending is made more difficult by the inclusion of "well-crafted". So we must attacked the nature of the delivery. A "well-crafted" speech would never appear insincere, but a delivery with an air of fakeness would qualify for fake gravitas. "Without the standing to deliver such sentiment".

Many ways to drive home what you mean, but to use a single word makes it difficult.