As Adam has indicated in his comment, powerhouse is often used metaphorically to indicate something which is known to be strong or powerful in some respect. As Merriam-Webster defines it,
2: one having great power: as
a : one having great drive, energy, or ability
b : an athletic team characterized by strong aggressive play
- The country is an economic powerhouse.
- Their company became a powerhouse in the video game industry.
- She's a powerhouse on the tennis court.
Here, Russia is described as a former growth-powerhouse, that is, a powerhouse of growth or a powerhouse when it comes to growth. In this context, growth refers to the phenomenon of economic growth, which EconomicsOnline defines as
an increase in the output that an economy produces over a period of time
In other words, Russia was known in the recent past for being reliably capable of strong economic growth. Their economy has slowed down lately, however; they are no longer known for strong economic growth, but indeed are on the "edge of recession" (a contraction in economic output). Thus, the author argues, Putin feels more vulnerable as a leader, since his resources (and thus power) are reduced and there is greater risk of discontent in the populace.
The inclusion of the hyphen is a stylistic choice which helps reduce ambiguity by solidifying the link between growth and powerhouse; it is one of the standard uses for the hyphen but in my opinion, not strictly necessary here.