I have no faith in Elan's prowess in this situation, but if they are correct that values THRX's revenue stream at over $5.5 Billion. That would mean that THRX is deeply undervalued at today's price.
Your proviso with respect to ELN is on-target, IMO. It makes more sense to interpret this deal as ELN overpaying for a portion of THRX’s royalties rather than THRX being grossly undervalued.
ELN could probably have done better for shareholders by accepting the buyout bid from Royalty Pharma or by closing shop and returning its cash to shareholders.
Royalty from THRX/GSK respiratory programs definitely COULD generate $5.5B royalty to THRX. The problem with ELN deal is it only includes FF/VI, UMEC/VI, MABA 081 monotherapy, VI monotherapy, not any combination of MABA 081, nor UMEC/VI/FF combination:
The transaction does not include any royalty participation interest associated with UMEC/VI/FF, an investigational medicine also in development under the LABA collaboration with GSK.
......
The transaction does not include any royalty participation interest associated with MABA ‘081 in combination with any other therapeutically active component, including an inhaled corticosteroid, or any other MABA compound as monotherapy or in combination.