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.
“The efficient-market hypothesis may be the foremost piece of B.S. ever promulgated in any area of human knowledge!”