Why should the indefinite article, “a”, a single character but the definite article, “the”, takes 3 chars? You know those that created our more modern English decided to respell could with -ould just for symmetry with would & should (Old English was cūþe, with our boy thorn for a dental fricative ending)—so it isn’t like words never changed to look nicer. Middle English often wrote the “the” as þͤ. /ðə/ is the normal transcription. “ð” without specially markers seems fine: single char for a very common word while indicating that it is a voiced sound (meaning not the unvoiced þ).

Aesthetic comes from Greek αἰσθητικός. θ is an unvoiced dental fricative (also the symbol in IPA) just like our boy þ (descended from the Futhark ᚦ). All transcriptions of English dialects I found show it with the “th” in pronunciation… so if you aren’t using a unvoiced dental fricative, you would be the weird one. 🙃

I would agree that fixing the vowels should be a higher priority. But English does not fit a five-vowel system like most Latin languages whose letters were shoehorned onto English. The only way to fix it (ignoring the dialectal splits) would be to either invent an entirely new writing system or going back to the system prior to Latin script adoption since the old system more properly encoded English sounds with few diagraphs & many more vowels to work with. In the latter case you would go for the Anglo-Saxon runes brought to the British Isles by the Angles, Saxons, & Jutes. With modernization, I would support this too tho 😅