As the title says: Why is e.g. 靴を脱いだとしたら、家に入り下さい considered unnatural and 靴を脱ぎ終えたら、家に入り下さい is the more natural way of communicating “Please enter the home after you have finished taking off your shoes”
If all V[過去形]としたら are unnatural usage — what is the deeper grammtical reason for it being unnatural?
That’s definitely not a typo. たら tends to work to explain a succession of events as used in the example above. It’s like saying “once you’ve removed your shoes…”
So why isn’t it any of the other options?
脱いだとたん means something unexpected happened after you removed your shoes. Not applicable here.
脱ぎだしたら sounds like you forcibly removed your shoes, so it’s kind of weird in this case.
脱いだとしたら unlike regular たら forms which can work as both a conditional and a sequence indicator, としたら is used exclusively as a conditional. “If you happened to remove your shoes…” something like that.
There are many examples of たら working as an indicator of successive events.
宿題が完了できたら、遊びに行く “I’m gonna go hang out after I’ve completed my homework”.
It’s a bit of an overlap between the way sequential events are presented in English, and the versatility of conditional forms in Japanese, which may make this a bit confusing at face value.
By typo I meant the missing お in 入り下さい and not that 脱ぎ終えたら should not be the answer to the question. But thanks for your comprehensive explanation. That としたら marks hypothetical use only was exactly the bit of information that I was missing to understanding this. I thought that this had something to do with としたら being preceeded by a verb in past form.