Is it possible to defeat 1000 Archangels with just one Imp?

No, no, the imp is certainly not the same as "the best" :)
You probably don't even understand what you're writing: what do tactics or ballistics have to do with this? No matter how you position this 1 IMP, the archangel will still go first and kill it. The point is simply that the imp has a speed of 5, and if you add all the speed artifacts, it becomes 9; and if you attack an archangel while wearing "Cursed Armor" (the slow effect will naturally trigger), then whoever attacked will move first, but that won't work with a peasant :) Do you understand about this now?

won't work. Cursed armor casts its crap only when receiving a turn.
and as you wrote, upon attack, the archs go first. Nothing has been cast on them yet. Therefore, it's game over for the imp.

there is another idea. we are sitting in the Castle. and we have the artillery and tactics skills. the computer attacks us with 1000 archs. without a book (or at least without direct damage magic). since we have artillery, we are given a turn at the very beginning of the battle and we can cast. we cast force field. the imp is out of reach.
1st turn: force field.
2nd turn: berserk.
3rd turn: force field
4th turn: slow.
5th turn: haste.
now our imps are faster than the archs, who are uncontrollable. then we just implode them.

of course, if the archs are in several stacks, you can simply tear them apart with berserk.

it doesn't matter whether it's a writer or an imp.
well, there is plenty of time. it will take... well, that's why it's a theoretical problem.

4th turn

Added after 19 minutes
and solving theoretical problems is not that interesting. here is a task.
how to take out hero Aiden. all stats around 40. mana around 1200. has 7000 archdevils. artifact Blade of Armageddon. Badge of Courage (gives +1 morale, immunity to mind magic (blindness, hypnosis, berserk)) expert tactics skill, and other haute couture upgrades;)...
what we have: there is a Dragon Utopia on the map, which gives the Tome of Water and other artifacts for stats. there are 3 Castles, 2 dungeons, 1 tower, 2 swamps, 1 rampart, 1 stronghold, game time 29 days (a month + 1 day)
this task was solved in two ways :) all just to get the Blade of Armageddon :).