Not 100% sure what you're asking, but here's my take:
Hololive English is by far the biggest vtuber brand in the EN sphere. They are no different than Hololive main branch in terms of requirements, cut, etc. The rumor is that the requirement is 3 pieces of content per week during the first year, with the requirement relaxing after the first year contract is up. The girls have personal managers, no more than 2-3 talents per manager, with others in management handling specific tasks like sponsorships and music. Outsiders such as Nijisanji members have noted management support for Hololive members seems higher than they're used to seeing. While nothing has come out of HoloEN specifically in terms of growth requirements, sister agency Holostars EN members have stated they have no growth requirements and had never heard performance indicators mentioned by their management. Hololive EN labors under content restrictions that are particularly strict about copyright, both game and music, thanks to the main branch's disastrous experience back in Aug 2020 where CapCom came within one strike of ending Mio's channel permanently. However other than copyright and sexual content, their content is relatively unfettered other than by YouTube's Terms of Service.
Nijisanji EN came second for a while, but their viewership has been on the decline lately. It's difficult to measure if they or Vshojo are second in the EN space, though many of their livers still pull thousands of viewers regularly. While information on management has been scarce, rumor is each wave has one manager. I don't know of their requirements etc, but there was one case where former member Yugo leaked a manager speaking to him about view trends. It's unlikely stream time requirements are particularly strict, as breaks and infrequent content are common across the agency. Content restrictions are slightly more open than Hololive, but are still greatly concerned with copyright and PR, as is the case with most Japanese vtuber agencies. Many EN livers operate on the axiom of asking for forgiveness rather than for permission, though in many cases planned content and events have been shut down before they start. With one prominent termination, it became apparent that Nijisanji EN uses stealth suspensions (unannounced suspensions / fake "breaks") as punishment for content that violates their policies. Generally though, Nijisanji enjoys some management content support, some event support, and gets plenty of merch, compared to smaller agencies.
Vshojo has been steady even through some tumultuous turnover in 2023, with several of their talents choosing to leave for a non-vtuber-focused streamer agency. The main feature of Vshojo is that outside talents who signed to them directly own/retain their Intellectual Property, with Vshojo acting as content support, merch creation, and somewhat as an agency to attract sponsors. Kson also claimed that Vshojo does not take any cut of donations, and that the company's revenue comes solely from merchandise. Prominent members of Vshojo are signed to other western-style talent agencies such as UTA, indicating non-exclusiveness. Recent members such as Matara Kan have indicated that content support is high, with offerings such as promotion plans, commissions, budgets, all acting under the talent's creative direction. Henya was able to participate in the agency's 3d concert within three months of joining. Managers are shared to some extent, as indicated by Kura and Matara Kan sharing a manager, but likely not more than 2-3 talents per manager. The company also has content teams on contract for member projects. Content restrictions are basically non-existent, with founding Vshojo member Projekt Melody still streaming regularly on porn site Chaturbate. Vshojo is one of the few big western agencies that still allows full on react content, ignoring those copyright implications completely, or rather, leaving the risk on the individual talents.
Phase Connect is definitely a strong fourth in the EN sphere, especially in the last three months where individual talents have come to rival Nijisani EN in viewcount. The willingness of the Phase talents to talk shit about their agency has indicated a relatively open management culture. Restrictions are mostly around copyright and avoiding bad PR, though they are pretty relaxed these days. There are multiple managers per generation and also specialist management for things such as music. It's not clear if there are any content frequency requirements or growth requirements, but if there are the talents have never made any mention of them, and given their talents' relative openness I doubt such things exist. While content support was relatively thin in the early days, in the last year Phase has made great strides, providing a music budget, launching music projects, partnering with other companies for 3d capability, and offering similar merch to the big three. Gen 3 has gotten advertisements, animated preview videos, and covers at debut, so they're continuing to expand their spending.
Idol is likely the fifth in the EN sphere, thanks to herculean promotional efforts and rapid acquisition of remaining high-profile independent talent. They paid a great deal in ads and watchalongs for their two EN generation debuts, and their talents definitely have a great deal of talent. Management is active and generally supports projects or other content. However, little is known about their contractual obligations if any. There are definitely red lines on their content and behavior, as shown by Riro Ron's recent termination, but given that talents have done things like claiming to drink their own piss on stream, I don't think they're that restricted at all. As usual copyright issues drive much of what they don't do eg. direct react content.
e:
As for smaller agencies, yes, there have been plenty, both those trying to emulate the big 3 on a shoestring budget, and also those that basically offer nothing except the model. Tsunderia had almost-nonexistent management support and fell apart in 2022. Cyberlive had bad management culture and fell apart in 2022, and their successor independent project Aetheria fell apart in 2022 also thanks to member drama. EN-speaking Taiwanese agency AikoAir fell apart in 2023 thanks to mismanagement. Production Kawaii is still ongoing and struggling. Brave Group of VSPO fame very recently launched two EN projects V4Mirai and Globie, with VSPO EN coming, though both are still getting off the ground rumor is they get very strong management support with the most recent example being 3d only a month after debut. Many smaller agencies exist and are generally relatively low-support or too small to be worth mentioning.
However, the small JP and small CN agency thing where they have strict requirements or growth metrics is generally not a thing in the EN sphere. This is a legacy of a strong culture of independent streaming in the west. Most talents would choose to remain independent than join an agency that would exploit them for zero or negative gain. It's telling that there are fully independent vtubers on Twitch at the same level as Vshojo.
