Population of Tonga 100kMate they're garbage and so is Tonga at the moment.
Tonga and Samoa's success is totally reliant on all the heritage star players eligible to represent them being available and electing to represent them over AUS or NZ. Because they aren't producing any talent locally there's no depth beneath that surface level, which is about as deep as a puddle, and relying on those top heritage players isn't sustainable over the long term.
Both of them will be up and down, yo-yo if you will, teams until such a time as genuine, sustainable, development of the sport happens on the ground in the islands. But that development isn't happening because there's no necessity for it for so long as they believe they can rely on Australia and NZ to produce the lion's share of their talent for them. Is what it is.
Population of samoa 200k
islander population in nz and Australia ? 500k to 1 million
Tonga and samoa will never be able to produce a much players as the Islander diaspora
at least they are more choosing to play for their home nations in rugby league unlike in union where the all blacks raid them hard as to the wallabies