There is a decline. It’s not drastic, and doesn’t affect every tool, but it’s there.
The 1/4” hex screwdriver bits were the first I noticed. The Original German made ones were very decent, the outsourced ones (Vietnam?) noticeably less so.
Pliers - were not something Wiha traditionally made, and were made in Vietnam from the outset. They don’t seem bad, but I don’t own any, and as they’re the same money as Knipex for me, there’s no incentive to buy any.
Screwdrivers - seem still to be o.k. but they were always mid price / workshop grade tools anyway, and the best ones (acetate handles) have been discontinued. The hex shank with the flared tips are nice.
Micro screwdrivers - don’t know about the quality of the current ones, but the old ones, while “o.k” were never really top end. Again, the hard handle models have been discontinued, so you can only get the soft “pica” finish now.
Hex Keys (conventional ones, not T handled) - still seem to be good, I’d buy them without question, but they are made in Germany (at least the last I saw were). The Torx keys are particularly nice I think.
There are some tools (those “26 in 1”, or whatever, bit drivers) that seem to be specially made for the U.S. market and don’t seem great. Some tools (bit sockets I think) seem to be made for, and only sold in, the U.S.