All of them are not like they used to be in their prime years anymore. All of these are for a few reasons, like fierce competition from small to medium companies, a wider international market for kpop, social media influence, poor marketing strategy, changing of leadership in the company and also poor management and decision making. All of these lead to the decline that we all feel.
If we put album sales and revenues aside, the Big 3 is simply not as powerful as they used to be. They are still on the top but not really that wow or impressive anymore.
SM: The pioneer for big kpop company. They used to dominate the market all from bg to gg. All their older groups are extremely popular, not only among kpop fans but also, gp. Yet starting from 3rd gen precisely after RV, they started to go downhill. Exo was super successful and has lots of potential but, sm dropped them since 2018 when the competition with Bts were very tight and close. Rv is always being treated like their stepdaughter. It is a mess. Dream has a chance but has started to be put aside. Wayv? Gone. Aespa and Riize are probably gonna get their senior treatment right after they are big enough for sm standard.
YG: Nothing much to say because they don't have a solid background of history, like sm. But they having the biggest and iconic bg in 2nd gen and gg in 3rd gen make you think they know what they are doing. Funnily enough, they are not. From having bigbang to being the last in the bg competition among the big 4. Not sure what will happen to bm and if they able to repeat the success of bp with them.
Jyp: Just like Yg, there is nothing much to say but they are known as a gg company for their iconic gg with hit after hit. Twice save their reputation as the company started to decline during early 3rd gen. Itzy did great during their rookie era and suddenly boom, they have such inconsistency in their TT. Nmixx didn't have a chance since the beginning. Their gg growth are the slowest now among the big 4. Skz are doing good internationally but not much domestically. For now, Jyp are also the weaker in domestic market among top companies.
In short, they are not at their peak anymore, but it's nothing bad yet. If this decline continues and becomes more severe as a generation changes, then it will be a different story.