There is no reason to not freeze as long as you do the defrosting stepwise like you said, not allowing fresh air and moisture to condense on the cold substances, doesn't have to be hygroscopic to attract condensation. If you're talking about decades for tryptamines I don't think it's very easy to overkill. Vacuum sealing is good, but you don't always know how pure your product is and don't want to give any destabilizing conditions any chance.
Not only do reactions double in rate roughly every 10C or so, but for some there can be an energy threshold which means that temperature can be important.
Storing in solution is a bad idea for many tryptamines which do various things like N-oxidize, but if you insist, definitely freeze your ethanolic solution, maybe adding something like ascorbic acid helps but I can't be certain.
You're certainly right though that stability esp for temperature is very important and arguably at least as important as the storage temperature itself, depending on the conditions. The sudden heat wave can be terrible (so don't speed it up when you are trying to avoid that condensation), but I actually have doubts that sudden freezing is quite as bad. It's certainly not how I remember cryogenics.