SUMMARY I don't think my rationale can be put into words for this, but in general I think there's an issue with sorting alphabetically. I believe sorting alphabetically assumes that you already know where the thing you are looking for is, rather than trying to find a file you have opened recently (but may have forgotten the specifics of). In the case of chronological by default, you now also have the context of the order in which you opened files (e.g. you know you opened file B way back, so there's no way that anything before that file was opened could be the thing you were looking for) as well as a sort of breadcrumb trail for what you were doing. I personally think that if I am searching for a file and I already know its exact name such that I can parse the alphabetical list of recent files, I probably already know where the thing is or I could just search for it by name rather than consult recents.
Sorting chronologically in recent files/folders is already the default since https://invent.kde.org/system/dolphin/-/merge_requests/365. It is just that the other default setting "Use same view style for all folders" overwrites this. We want to disable "Use same view style for all folders" by default but this is unfortunately currently not possible because disabling that option leads to configuration files being created in every folder one visits which seems unacceptable as a default. So we all agree. The issues are technical. If my idea https://invent.kde.org/system/dolphin/-/merge_requests/288#note_384582 or something similar gets implemented we can change that other setting and then what is suggested here would be the actual default for everyone. Closing this bug report because it is sort of already implemented and not really actionable because the real problem lies elsewhere.