Would a sublingual dose be possible/more effective? Research in other (um, yeah, medicinal!) compounds shows that it can be an effective pathway to the bloodstream rather than trying to survive the digestive system.
Injection is really the only method with any substantial bioavailability. BUT, low (<1%) bioavailability does not necessarily mean useless.
Can you say more about that point ?
Injectable Semaglutide/Tirzepatide (>99.8% pure) are currently sold at a profit from China for around $2-3/weekly dose. Rybelsus (oral semaglutide) is sold at roughly the same cost per milligram, even though it's made in FDA-approved facilities (you just need to take >= 40x more milligrams per month, bringing it to $1000/month in the USA)
So manufacturing oral doses 100x higher than injectable seems to be economically viable.