I would put a huge reduction in investment as way higher than 30% - investment cycles boom and bust as does the economy. Even a global recession or similar could massively reduce AI expenditure while AI development continued marching on at a similar or only slightly reduced rate.
On the other hand the current crypto winter does match the OPs definition, with practical use of crypto reducing along with investment reducing.
In general though I agree with you that looking at investment figures isn’t a robust way to define a “winter”.
I would put a huge reduction in investment as way higher than 30% - investment cycles boom and bust as does the economy. Even a global recession or similar could massively reduce AI expenditure while AI development continued marching on at a similar or only slightly reduced rate.
On the other hand the current crypto winter does match the OPs definition, with practical use of crypto reducing along with investment reducing.
In general though I agree with you that looking at investment figures isn’t a robust way to define a “winter”.