Again don't disagree as you make a lot of sense and the req. are though. My guess is they're just looking to make it easier for more MNC's to setup a small shop, to ultimately attract them to expand buss. in TH (and attract knowledge, labor etc). Many ways lead to Rome and they selected this specific one?
I don't disagree with you. The targeted companies i.c.w. expected no. of LTRs don't make sense. At the same time I also imagine a thought process behind the requirements like 'big companies' having to do with a fair level of abuse they want to prevent, i.e. not have (paper only) companies just to get 'a visa'.
Mate, your statement "A work permit can be cancelled anytime, and thus it has no expiry date" is incorrect as extension of the regular work permit is required at Department of Employment (just like the non b visa).