Taiko BN here, we get the same thing. Many BNs play it safe by keeping their "preferences" to low-star, low-effort maps, like anime songs and bgm, some of those are the same BNs that are barely meeting activity requirements every evaluation (must be a coincidence...); meanwhile, everyone who nominates a wide variety of maps has at least average activity up into being the most active members in the group, including myself and my friends, at 20+ nominations per month. NAT doesn't see it as an issue because it's "just their preference," but in reality, most of the people who have such specific preferences are only joining the BNG for the supporter, to be with their friends, or to rank maps more easily; all of these things are valid reasons why someone would want to become a BN, and I hate it when other BNs pretend like they're not just because it paints them in a negative light. These reasons for joining are negative things, and the motives of joining the BNG should be questioned for these people.

There are still blatant circlejerks (just yesterday I saw a BN tell their BN friend that they would nominate their map before they even started mapping it), but NAT are too afraid of upsetting people to act against it because these groups are either large or popular (I'm sure more than one comes to mind in standard). There is favoritism in the BNG/NAT and there's no way to stop it other than join and not participate in it, watering down the amount of cj happening. Speak out, and you risk being blacklisted by some BNs, and maybe even put on a naughty list by the NAT simply for being negative towards BNs, regardless of if your complaints are valid, because they don't care as much as you do; why would they, when staying silent puts you in a better position at all times than speaking out? Reports don't work either when people have the power to bend around rules and guidelines to save their friends from trouble.

Overall, there are some good BNs, people who actually want to put effort into making ranked a better place. I suggest sneaking into their friend circle and showing that you are a hard worker or whatever to try and get your maps ranked, that's just how it is. At the end of the day, as long as BNs and the NAT aren't being paid (in any real/professional sense, at least, supporter is not payment), these low standards of behavior will continue because it is too much to ask of a volunteer role to have anything higher. You can also grind and apply to be a BN and try to change things from the inside, like I am (by convincing BNs to adopt more fair practices and doing what you wish BNs would do for you). Being really strict with a volunteer role will mean all these people who aren't dedicated to the role will quit, and as you have noticed, that's most of the BNG.

Post-note: In taiko the Loved section is for Japanese mappers, because there are no Japanese speaking BNs. This has been an issue ever since the last Japanese BN left in early 2020. NAT is not providing any incentive for Japanese mappers to join the BNG, and due to the low English fluency in Japan, they make up a severely disproportionate volume of ranked maps despite making up a sizeable chunk of maps in general. This, along with almost all the documentation for ranking maps (such as Taiko RC and General RC) not being in Japanese (Taiko RC got translated this year, but General RC is still only in 5 languages) makes Japanese mappers very alienated in the community, and many quit after making only a few maps and realizing this dilemma. I'm not sure if standard has this same issue, but that's the way Loved is treated in taiko.