I think a better way to approach this is making the bosses more accessible to newer players. There is a pretty high bar for entry on nex, grae and harb if you want to be actually farming it for drops. Granted these give you the best gear in the game and shouldn't be able to be farmed by anyone and everyone, you should of course have to put in some work gearing up for it. But I'm thinking that on the path to get this endgame gear, the bosses should be doable in the next best thing from a lower tier boss.
Harb and Grae aren't so bad in my opinion, the main barrier for harb is a divine which is kind of rare but not impossible to get your hands on. Grae just has ridiculous amounts of HP and would really benefit more from group farming on the lower levels. But I feel like a lot of players end up just doing their own thing.
Nex however has the dumbest fucking defence I've ever seen. I have a clip from years ago where me and zarpor josh were messing around and decided to duo nex with maple shortbows. Granted this is on rs3 with abilities and shit, but we did it in 9 minutes, that's about the average solo here in max gear. It shouldn't take more than 5 minutes for a duo in moderate gear. Much like grae I believe newer players would benefit from grouping up on nex to get these drops into eco but the barrier for entry is pretty high right now.