Makes perfect sense on a cursory level and you're not alone in thinking of it that way, trust me! Although I don't think Argentina should be on that list, their best players are committed to the Premiership/Top14/Rabo and I'm pretty sure most of their 7s guys are club players back home.
The best Samoan players are also generally contracted out to European clubs or even Super Rugby.
Going to play a bit of devil's advocate to your hypothesis here with this video:
When you consider how they were performing at the time of this video it stands as a testament that you don't need elite facilities to build an elite, or at the very least competitive program. I personally was impressed with the 5th place finish of Kenya at the end of the IRB 7s. For reference, Australia finished 8th last year.
In terms of player resources I'm not sure if that holds up entirely as a performance-related argument here. I'd be
very surprised if Kenya has anywhere near ~38k senior male players like Australia (
http://intheloose.com/wp-content/uploads/2014/01/IRB-Player-Numbers.jpg). Samoa and Canada both have less than 10k senior males, although Canada may have grown since 2011. Hard to really gauge because RWC time also tends to inflate playing numbers due to hype surrounding the tournament.
So, for the sake of an entirely unscientific thought experiment let's round these numbers to 40k senior males for Australia and 10k senior males each for Kenya/Samoa/Canada. Let's assume that each nation has a roughly equivalent pool of genetic material to pull from that generates "elite" rugby athletes (pure pace and athleticism absolutely has more weight to it in 7s than 15s, I know coaching and a lot of other things are factors too but like I said, entirely unscientific) at a rate of 1%.
This would leave Australia with 400 "elite" rugby athletes and the other nations with 100 a piece. So while Australian 7s does compete with Super Rugby (and even other codes) the sheer difference in playing numbers
should do a lot to make up for this if you look at it from a purely numbers perspective.
That long-winded bit behind us, I think a lot of the Thunderbolts problems have to do more with what happens between whistles than it does any outside factors. With Vegas in front of mind, just a few less missed tackles and a quicker restructuring of the defensive line and the Thunderbolts would likely have had an entirely different outcome by the end of the tournament.
