I'm in one of these so called small/mid firms. Any idea why you're particularly interested in this tier of firms?

It is true that mid tier firms are losing ground due to industry outlook. Legal market isn't doing very well. Don't be wowed by the lay prestige of lawyers. There is a stratification in that the top tier (big 4 and internationals) will continue to get cutting edge transactional work, and the mid tiers fight for all the smaller deals that remain. there is a lot of undercutting in fees and this translates to lesser partner earnings, which means lower associate pay and/or letting some people go.

in fact, this trend mirrors the global legal industry in other markets as well, e.g. UK and USA.

all this is of course contingent on the assumption that you want to do transactional work. if you are looking at litigation/dispute resolution, its not so much the brand name and size of the deal, but the experience that you get when working on cases. many good litigators started out in lesser known firms too.

as a trainee, if you can get into a top tier firm for transactional work, good job, provided you can stomach the hours. the mid tier's quality of life is better, but the brand name (or lack thereof) will set you back if you're aiming to be a top flight corporate lawyer.

as for "sunset firms" or not, this is beyond your payscale (apart from impacting your hiring or retention chances), and once you reach a level on the payscale where it actually concerns you, you'll hopefully have options to move around for greener pastures.

still, nothing is set in stone. even some corporate partners in top firms and ranked on IFLR, Legal 500 etc have come from humbler beginnings. once you reach 3-4 PQE, you have options - its how you spin your experiences and CV.