you are missing the complete point
I'm not, we're speaking about the same thing.
people wont know of the rate change while using LN.. they see the msats and dilly dally happily moving msats in onion payments
.until.. they broadcast the commitment and see onchain that they are getting not as much as promised.. [emphasis mine]
then you will see
I acknowledged that you can indeed lose 1sat. So yes, you're wrong with the bolded sentence;
they may get up to 1 satoshi less than the msat amount in their wallet.
Although, this is nothing new and nothing to worry about; 1sat is worth $0.00016USD or 0.016 cents.