Name any base level character that is still relevant even with a full skill trial. Maybe in some minor event or something like Zenith where you have to use low end characters. Anyone that was completely breakable by Elite Sweeps or useful at the very beginning treasures of the game aren't that great. This is kind of by design anyways. "Premium" ninjas are better than free/starting ninjas.

Personally I rather see Susano Itachi get his trials first. That would probably be more useful in the current meta. Since things like his Standard are already undodgeable, super armor, immunity, etc. He would only get way better. Edo Itachi's trial is already better than likely anything that regular Itachi would get anyways. So if we do get any more trials, cool. He'll probably be fun to play around with. But otherwise IMO it's not a super big deal right now. Plenty of other better ninjas are about to get their trials here soon anyways.

Weaker characters are always less of priority. Characters will get them eventually it's just that "premium" is more of a focus to the company because it makes more money.

Example is the latest trials in CN is Halloween Kimimaro. A "premium" ninja. Ringo was a while before that. Eventually they work down the tier list. Ninja like base Itachi is way down the list.

I'm being objective. You just don't like the answer. The same applies to every character. Zabuza, Baki, Temari, for example, all never even got any new skills yet. Eventually they will. It's just not a priority obviously. So all we can do is wait.