Fiji, Samoa, and Tonga haven't fallen off, they were just incapable of keeping up with the growth in other nations because they're tiny, impoverished, third world countries whom can't compete with size and resources of some of the other nations. In other words they're not getting worse, Japan, Argentina, the home nations, Gorgia, Italy, etc, are getting better.
The only thing you could actively do to make them more competitive would be to further bastardise the eligibility rules to them even more like RL's, but that would directly impact the Wallabies and All Blacks, they're both more valuable to WR than the PI's.
RU's current struggles in England are irrelevant from the point at hand, they're also largely a result of bad private equity deals. Will English RU take a hit for the foreseeable future; sure. Will they need to restructure to make sure they don't make the same mistakes again; definitely. Will it kill or cripple them anymore than they already are over the long term; no, it won't even drop them to RL's level in England.
I wasn't ignorant of them either, I addressed them in the post you were too lazy to read...
League One, Top 14, the URC, etc, aren't going to fail anytime soon...