I saw in another article the problem for them could be onward connections from LHR or AMS or CDG, but B6 could look for codeshare partners.
https://airwaysmag.com/airlines/jetb...-market-entry/
Unless they're going to try to code with RyanAir or EasyJet, I cannot imagine BA, VS, KL, AF, LH, et al coding with them and harming their highly profitable JV's.