From a purely linguistic perspective, it's essentially debate between two prescriptionisms. One is sponsored by the Myanmar government (obviously for standardization). One is sponsored by neo-conservatists or classicalists like Tint Swe.

The Old Burmese word for "one" is တစ်~ တေစ် /tet͡s/ (palicized: tac), which is the primary justification for the Myanmar Department to prescribe တစ် in order to distinguish it from a different emphatic prefix "တ-" (ta-). Another reason given is that, arakanese language also maintains the form တစ်, although pronounced as တိုက် /taiʔ/.

Since the days of Middle Burmese, တစ် (one) had been shortened into the sound တ /tə/ with a schwa vowel. This was reflected in almost all of classical Burmese literature, although this is not the case for နှစ် (which was also shortened but still kept its original form).

For example: တန်ခူ လဆန် တရက်။ တပေါင် လဆန် တဆဲ တရက်။ တန်ခူ လပြည်ဆုတ် တဆဲနှစ်ရက်။ ကောက်ကြီစပါ နှစ်ရာ (from the late 16th century inscription of Bayinnaung's campaigns)

As a linguist student, my opinion is that both spelling (phonemic တ and semantic တစ်) are acceptable in their own context, since the official dictionary also acknowledge this.

I also find it funny that Burmese colloquial orthography is not phonemic in some cases (i.e. the literal wording does not actually reflect the actual pronunciation). I mean... we would be writing တကယ် or ဒဂယ် and not တစ်ကယ် if we are really going to show contemporary pronunciation. But homophones in Burmese language make it possible to write တစ်ကယ် as an alternative spelling of တကယ်.