As someone who became a fan in '82, I don't really have a problem with Doctor Who being shown on other days, although the Tom Baker era does remind me of Saturday tea times as a young 'un. (In those days, with one telly and no remote control it depended whether other members of my family wanted to watch it. Generally, post 'Talons...' they didn't! So missed out on Season 16, etc completely. Now one of me favourites.) *
But.....I agree that moving the programme from where it's been since 2005 is unnecessary. It's doing fine in the ratings, and if/when BARB factor in BBC1 + 1 and increase what i-player 'hits' they take into account (think that's on the cards?) the 'officials' will more likely than not look even healthier.
Also, it just 'feels' like a Saturday rather than a Sunday type of programme. Sunday feels like a more Midwifey, Midsomery, heartbeaty, All Creaturesgreatandsmally sort of day, y'know.
*That sounds like they hated Talons! Told in retrospect they got a bit fed up with Tom in the part. Ridiculous, I know!