Hi,
It probably won't be too broken.
At 4 points, a Feat is valued as 2 points of attributes above 13. To maximize the value, we might expect a character never to boost attributes below 13 using future ASIs.
Most spellcasters want a casting stat, Dex and Con to be high, and they rarely need many feats, except for Moon Druids and gishes. Is starting with Con proficiency worth it for casters? If so, it's not overpowered. Gnome Abjurers might like casting Nondetection a lot.
Moon Druid: The only stat you deeply care about is Wisdom, since you hope to spend lots of time in animal and elemental forms. But when you cast, you're in normal form so you have to care about Dex and Con a little bit. You also have to survive level 1. Alert, Sentinel... there's a druid guide somewhere.
Archers don't care about Str, and since they hang back maybe care less about Con too. So, start with Sharpshooter and maybe Crossbow Expert?
A melee Fighter might want to make room for things like Heavy Armor Mastery, which is at its best at level 1. But GWM and PAM are also party favorites.
A gish might dump his two mental non-casting attributes and one of Str/Dex to 8, to make room for Warcaster and Proficient Con. Etc.
I'm not seeing anything scary or broken. But you are likely to see more ruthless dump stats, to make room for narrower specialization. I'm not sure if that's a good side effect, though I don't think it's broken.
Anyway,
Ken