Suna is the weakest village, period. At every time when Suna's strenght is mentioned, it's basically the tale of how it lost power in one way or another.
Baki said that the Damiyo followed a demilitarization policy that backfired. Means they lost funds, lost shinobis, lost structure to teach them etc etc etc remember that a hidden village is essentially the Naruto-world equal to a military citadel, they need losts of funds to sustain themselves. Suna lost that funds long ago.
They had only one beast (it's not the weakest as the tails=strenght equation is declared false by 8-Tails) and since it had a really bad attitude, no one ever managed to control it half-decently, that includes Gaara. Is actually implied that in attempts to control the 1-tail they lost more power than they gained.
Two of their kages got assassinated, huge loss of military power; especially about losing the third, remember that it is implied that when the third world war occurred, it was also due to Suna scattering shinobis everywhere looking for the third kazekage and getting assaulted by all the other countries at once... again, huge blow at their resources. Magnet release is basically eradicated from Suna altogether.
They lost Pakura, a war hero with a unique, devastating kekkei genkai that essentially kills on touch AND on distance, handling her over to an opposing country - it speaks of how desperate they are looking for alliances. Like with the Sound village and later with Konoha village, it's clear that they repedeatly seek to strenghten diplomatic relationships with powers greater than their own. Scorch release is probably lost universally since Pakura was named after that style.
The prized puppet brigade is disbanded, Chiyo was retired, Sasori defected and turned against Suna, Mukade defected and time-travelled away, Monzaemon Chikamatsu is long-time dead. Kankuro is basically the only strong puppet user left. Most of the strongest puppets made (Kankuro's, Sasori's, Chiyo's collection) have been destroyed through the series.
All one needs to do is paying attention to the anime and manga - it's made pretty clear that Suna is the weakest village.
Before anyone says I'm a hater, it is also my favorite village and my fav character hails from that village. It doesn't make it stronger, sadly.
I'm interested to see this.
