Would apply in homecountry, then less hassle to get documentation approved, and no travel expenses to a 3 country, with nothing else to do that wait for the visa.
Go to the “important” meeting, but then you probably would be rejected, loose the 10.000 baht visa fee, and have to do a new application, and again stay in another country for a week or two, with those travel expenses that will bring.
In most Embassy website, they clearly state the no reason wil be given, if application is rejected, but with all those requests for additional documents for the same reasons, it should give you a clou why.