Don't be silly, weapons do not deteriorate THAT fast, unless they are unreliable/fragile. Armors? Maybe, but that's because they are taking hits.
Fragile means that a weapon will deteriorate 25% faster.
The new system has quality levels IN ADDITION to the Fragile and Durable (deteriorate 25% slower) weapons traits.
As near as I can tell the Quality levels are:
Perfect (deterioration is one quarter of what it was before Quality was introduced)
Outstanding
Cool
Better
Normal (deterioration is the same as before Quality was introduced)
Bad
Very Bad
Garbage.
We don't know what the deterioration rates are for Outstanding, Cool, Better, Bad, Very Bad and Garbage are. We only know that deterioration rates increase going from Perfect to Normal and that it would be reasonable to assume that deterioration rates increase going from Normal to Garbage as there would be no need for these Quality levels if they didn't. Based on what we know, a Durable weapon with a Normal Quality will deteriorate faster than a Fragile weapon with a Perfect Quality. Basically, the deterioration rate for even a Durable weapon of Garbage Quality would truly suck. So yes, a weapon might deteriorate THAT fast if it is Garbage, even a Durable Garbage weapon.
A weapon can be taken from Perfect Quality to Garbage in as little as seven repairs. Now, how often you will want to repair a weapon varies from person to person and weapon to weapon, but everyone should want to keep the weapon above 75% to keep it functioning at full potential.
However, all of this will become moot, if and when the method of upgrading Quality is introduced that John Porno mentioned.