I hear ya and I get what you say. But I think 3.5 has been handled so badly by Funcom and well, me and my raid group are now going through T5. We did have some nights in 3.5 and killed potato man a few times and some wipes on Zaal, but then T5 was released
Would love to to try Lurker some day, but it's not gonna happen.
Basically, as I see it, one would have to jump ship and join one of the few top raid guilds to maybe see these "cool but not popular" bosses. And that's why I enjoy 6 mans more lately (it's just free of those practical problems that comes with relying on 24 people).
So far it's also fun doing T5 progression despite it being recycled content, but... I deffo don't feel like I did when we progressed through T4, now it's more like "yeah hopefully it dies at some point".