In to out swing path - how much is too much ?

it kinda depends OP (ball starting direction, curvature in flight, down to strike location on the face and the relationship between the face angle and the swing direction of the clubhead (swing path) at strike)

but if an in to out path tends to get more to the extreme, so say as a guide starting to get upwards of 6º+, towards around 10º
then the face angle closure rate is going to have to get quicker in a shorter distance as the clubhead nears the ball which is a deal harder to achieve consistently so a player becomes more reliant on timing and hand/arm action

plus if 'too much' from the inside the more shallow the arc will be, the AoA into the ball which will lead to fat contacts, which can then mean the player often times then stands up some into impact, early extends, with the arms moving a bunch out and away from the body with then high hands at strike with a steep shaft angle which can also lead to a bunch of toe strikes

if a player has repeatable good timing swing to swing and the swing path is say 6º/7º in to out and is also able to manage the clubface angle relationship to that swing direction (path) at strike plus center strike then they will get flight that moves a consistent distance right to left so it's still possible to play pretty good with that

as ever with golf it's a relationship with a bunch of impact conditions and the swing motions to produce those, but the more to the extreme ends of the scale of stuff the more difficult it can become to have a more consistent set of shot outcomes