I wonder if Snopes has an article? I’d say plausible.
Honestly, I think manufacturers make a big deal out of a lot of things that might make a 1% difference.
Think of this - your scalp acts like it’s own slip plane MIPS liner. Your hair, if you have it, also acts like a MIPS liner. It’s not like helmets are locked solidly on the head. They will naturally move and provide a slip plane.
You also wonder whether helmets are designed to provide the best possible protection or to score the best on a certain test. MIPS helmets score well on the Virginia Tech test because they prioritize the slip plane but there are still lots of 5 star helmets on their list that aren’t MIPS or Wavecell.
My latest helmet is MIPS (I don’t intend to crash test that) I have crash tested a few KASKs in the past though which do not MIPS and touchwood its they’ve performed well. On my limited experience you don’t need MIP (no harm in it though)
If you read the topic, the answer is still the same. There’s no reason to replace a helmet on a schedule. The materials don’t degrade in such a short time frame. If it’s in bad condition or been crashed, then replace it.
I think I had the Oakley since 2018. I replaced it last year which was coincidentally 5years but because I fancied a new one Id saw with a magnetic buckle. Which has turned out to be a great choice for me. I got a plain white Ekoi AR14 for a good price a coloured or team branded one was 2-3 times the price.