In the end, it’s all subjective but – if you’ll hear me out – thogh doesn’t alter the current spelling very much while maintaining a linguistic heritage (as the “thogh” spelling was also likewise used, during Middle English); also, the number of words ending in just the “o” vowel is less common, I feel, and will probably look doubly foreign to a native English speaker due to the consonant digraph (though, again, subjective; maybe not).

However, – additionally – saving “oght” for “thought” is giving that letter combination a sound already covered in English by another letter combination: “aught” (e.g. caught, fraught, taught, …thaught…?). If we’re keeping “ogh” around, we might as well give it a unique pronunciation association to avoid the overlap that was the original problem with “ough”.

Finally, a single “f” for “tough” could work (certainly, there are examples) but we miss out on employing the Germanic linguistic tendency to indicate a short vowel sound with a double consonant, inherited by words such as “ball”, “fall”, “doll”, “call”, or “puff” (of course, there’s plenty of exceptions (“get”, “bet”, “mat”, etc.) but, so long as we’re making changes, firming up an existing rule (and avoiding the brief uncertainty of whether or not the reader is dealing with a prefix) would, arguably, be useful).