Trade nerf, something isn't right here for the Mongols

So I looked up at the trade nerf that went 25 to 30 seconds production time, the thing is for some reason the 5 seconds also applies to the silver tree, making it 21 seconds instead of 18 seconds.
Isnt the 40% faster production supposed to be on the silver tree after the 30 seconds? for some reason they didnt include it on to the silver tree.

Seem like system calculate as below:
Narmally: [25] + 5 = 30 sec
Silver tree: [25(0.6)] + 5 = [15] + 5 = 20 sec

Dev just add 5 sec after every market.

This make absolutely no sense as the current patch will ve irrelevant in a year and the description says 40%,
not 40% prior to patch 9.x + 5

Also it’s 21 not 20 , that’s exactly 30% instead of 40%