@Adam I would say languages have this tendency to become simpler that you notice: some things are regularised and dropped off.
At the same time, they have a tendency to become more complex, when things are contracted to become unrecognisably more irregular
And there are other mechanisms.
So the Romance languages have lost some complexity from Latin, but gained some, too.
For example, the role and importance of word order might be considered a newish complexity, or the use of prepositions, or many other subtle rules.
An example of how Latin became more complex: I believe some scholars argue that e.g. the dative ending (originally -i) was once more like a particle or postposition or even praeposition, but it slowly became enclitic and eventually attached to the noun, then finally became a case ending.
And then the ending became less regular because of phonological changes.
@JoonasIlmavirta True it's likely English only seems simpler to me because it's my native language. I've heard English is more challenging to learn for non-speakers.
I suppose it's all subjective unless there's a consistent way to define what "more complex" is, anyway.
@Cerberus Is a case ending more complex than a separate particle in a highly inflected language? I don't actually know, just wondering. 😅
@Adam Yeah. For pretty much any pair of languages it's easy to find metrics making one or the other look more complex. The difficulties are in different places.
That could actually be fun, playing it as a coöperative game.
@JoonasIlmavirta Uhh I should not think so?
@Adam Generally, the endings of a case tend to be not always the same, depending on the stem of the noun. And they may merge or contract with other endings/suffixes into something less recognisable.
@Cerberus I faintly recall reading somewhere (probably on this site) that one theory for the origin of the passive -i is that it is originally a dative ending. I can't remember details, and even if I could, I couldn't judge them.
@Cerberus It resets 7 pm Finnish time. That should be around 6 pm for you and noon or 9 am for the US coasts.
I don't want to start a new game too late and take the risk of not finishing in time. Something within fiveish hours of reset should work for me on most days.