For my application, I'm still happily using gemini-2.5-flash and the only problem is when it reports being overloaded. It's for interpreting a downscaled phone camera photo of a hand-written shopping list on a whiteboard, and it works stunningly well. My handwriting sucks, too.

(I guess the only relevance here is that if your problem matches a model's strengths, then you can do fine with a model that is several generations out of date.)

I believe the older models are being gradually phased out, newer ones have no availability issues