I do know when the greenhouse dropped in humidity, I had more problems with leaves getting "stuck". Like they wouldn't unroll correctly.
Maybe someone from Arizona or another area like that could answer that better, though.

Here in south Louisiana we have very high humidity and bananas do very well.

Bananna's also usually do VERY well here in Alexandria, VA ( a couple miles from downtown Washington DC right on the river) from may through october. I have seen them survive as late as mid to late November in more protected areas/ southern exposures.

I have been growing them for about 6 years here, and they seem to LOVE the hot, HUMID summers we have. At times I will have to water them DAILY to keep up the good 2 leaf/ week growth. They do suck up LOTS of water, even if they are in the ground. My Bananna last summer got to 16' and it survived until the beginning of November. I did have to water it every day though, espeically during the hight of the long hot summer days, when we may not always get enough rain.

Our rainfall is usually over 120" a year and the humidity is usually up around 95% or more and bananas just love growing here. They like moist mucky growing conditions so I'd vote for the more humidity the merrier.

Bananas are indigenous to the Ecuatorial parts of the world, they like it hot, humid and wet; they grow best between 75 and 90 degrees and the higher the humidity the better. I live in South Florida and grow 6 different varieties and come Oct. thru April when the humidity is lowest, they grow the slowest.

My super Dwarft has grown more leaves in winter in Pa. Indoor , than without( a leaf a mo.) with added humidifiers. Winter it's hard to get a leaf or roots to grow even in sun & water & food.

Since banana trees are native to very hot, humid, and tropical areas, humidity is a very important factor and may even mean the difference between life and death.

All that surface area on the leaves mean lots of leaf to transpire water. Dry air will make that worse, requiring more uptake from the roots. Many plants (like say nepenthes) can't adapt to arid conditions - they just die. I would imagine bananas would be the same, though in general they seem pretty tough. They just do better with more humid, wet, hot, sunny, tropical conditions year round. I would bet that if someone tried to grow them in the badlands or say in the Sahara or gobi desert, the amount of irrigation would not matter - plants would be dead without some serious intervention.

Mine slow way down during my south Florida winter. I'm sure some of that is the declining humidity, while most is probably the dry season, and lowering temperatures.

It seem after I used cold humidifiers until feb. 1,it looked like all my beautiful roots were gone ! I couldn't believe they looked So good feeding every mo. Grow bulb & humidifier but humidifier was what started to rot I think. I ordered micro organisms , I hear hell root better than rooting compound we'll see if it gets here in time to save. The two!

Wind also increases the transpiration rate therefore, all else equal, a banana plant will grow better indoors. I have seen banana leaves scorch and die from dry winds but never from still, dry air.