The speaker, a 魔術者, is talking about the process of manipulating a man to do something advantageous for the speaker. The exact particulars of how this was done were never mentioned, it just was done.
For the sake of increasing the success rate, an appropriate amount of time and effort needs to be spent, on top of that, "to produce a large reaction (total guess)", there is often a substantial burden on the practitioner.
Brainwashing and disciplining via words is effective in the long term ぐらいだ
Though in this situation, for the purpose of a pinpoint dosage of manipulation, depending on the method (魔術 or 言葉?), it is also extremely effective (sometimes?)
There is definitely something that I am missing between the 2nd and 4th sentences as a congruent thought process is not maintained.
How is で used in 反動で大きな反作用を招いて and how does it work in relation to both 反作用 and 反動 in such a short span?
This may be contingent on my lack of understanding of the 2nd/4th sentence, but I can't tell why mentioning the extent of ...の方が長期的に見て効率がいい is relevant in this context.
Again this may be relating my misunderstanding of the 2nd and 3rd sentences. In the 3rd sentence, I have an issue with the disconnect between やり方次第で and ~たりもする. やり方次第で implies an outcome depending on the method but 有効だったりもする indicates a good outcome among other things. So does that imply depending on the method, it can also be not effective? Or what is the scope of this ~たり statement? In addition what is the also/も relating to then?