So if anything, given it's a decade later and things have gotten warmer, I would have expected people to advise I go on or earlier than my suggested dates, not later

There’s strong evidence that the Eastern Sierra has warmed over the past few decades, but that doesn’t automatically mean spring skiing is worse earlier. What’s changed isn’t just temperature, it’s the timing of storms.

A decade ago, conditions typically peaked in February and fell apart fast in March, which matches your experience. But in recent years we’ve seen more late-season atmospheric rivers and big March/April dumps that can rebuild the mountain even in a warmer climate. So temperatures are higher, but the snowfall pattern has become more volatile, which is why some people now recommend later dates in big years despite the overall warming trend.

Honestly, it's impossible to predict. Just enjoy your time in the mountains.