DTV is a very wide-ranging visa and covers many foreigners' situations. I switched last year from non-O visa to DTV, after being on non-O for several years. The DTV is a cheaper and more flexible option for many, especially those who travel overseas a lot. What you describe as the "correct visa" depends on the individual circumstances of the applicant. The DTV has enabled many retirees and those married to a Thai to switch to a more suitable visa for their own situation, which therefore makes it the "correct" visa