Yes, but it is generally thought that seniority is linked to age. If BA is used as an example (and it will) then clearly there is an indirect link between seniority and age. If a relatively young suitably qualified and experienced FO in BA sees a command opportunity come up and fails to get it against someone with high seniority through a system indirectly linked to age then they are likely to win an ET. Likewise, if a very junior person in a company like BA challenges the fact that they aren't going to get a weekend off in their first 8 years due to a seniority based sytem then they are likely to win. This applies to many other companies.
I am sure the lawmakers would be willing to acept a compromise alternative system which reflects the complex and to some extent unique situation in this industry where Commands also carry a legal responsibility. It could be argued that the application for a comand could be regarded as an application for a managment postion rather than shop floor - Now there's a debate.
The industry and Unions could come up with a sensible compromise which would be acceptable, but I can understand the sofar head in the sand approach as it will be extremely complex. Wait until someone makes a challenge and then see how it goes seems to be the general SOP in this industry.
Also, this industry is rife with the funny handshake and old squadron tie brigade so without a massive culture shift, it is unlikely that many companies could manage to put togeter any sort of fair merrit based system. it probably works OK in easy where there is a shortage of qualified FO's, but how would BA select Captains based on anything other than seniority. Seniority lists are far form ideal, but until there are new workable systems in place (at great cost to the beancounters) then they are all we have.