It’s difficult to explain this, but you’re wrong, there is no regional dialect that would pronounce the word this as this, because it is awkward.

Both are interdental fricatives, but this is always done with a voiced dental fricative, a voiceless would be the way people pronounce thistle. Now try to say this place but say this without the le on thistle.

I’m on mobile and can’t type out the IPA symbols, but I did take linguistics classes so I know the difference between the two phones, whereas you seem to equate the phones with their orthography.

They absolutely do not

You can only stretch the firmament so much before it tears