I don't know if I'd claim there was much favoritism at Phase Connect, beyond sponsors wanting to make use of more popular talents like the upcoming SWPN concert. The Gen 1 talents all have two models each, even the JP girls who are under 20K subs. All the talents get pretty good merch support for special events. Tournaments like Idol Showdown and Mahjong tournament have a mix of older talents with a lot of subs and newcomers with lower sub counts. And remember the con where they only wanted a few of the more popular talents, but Fishman gave an ultimatum that all the talents were invited or Phase Connect wouldn't attend.For that argument itself the only circumstantial evidence we have is that Fishman doesn't treat all talents equal, in a sense not every one get supported like Lumi, Pippa or Tenma. Not in a meritocratic way, but in a "I guess you're the one starving" way.
If I had to make an educated guess, the new contracts are much more advantageous for Phase than the talents when compared to the ones who joined earlier, and this could come from Fishman noticing his own naivety and biting them in the ass as business usually go.
We would never know for sure without a talent burning their bridges and they might be happy with how little they gain from it. It's all about self-respect and awareness, I guess.
You might be able to point at stuff like Rie having lots of covers compared to other talents, or Lumi having more models than other talents, but I think there's a lot of back-end work that gets traded for that. Anyway, we all know that Jelly is Sakana's favourite talent, but it doesn't really look like she gets anything above and beyond what the other talents get.