Looking at the table at the bottom of page 135 in Xanathar's we get the suggestion that a party of level 10 characters should have a total of 1 rare major item.
Since a +1 armor is a rare major item, this gives a total of 1 armor for the whole party. Or none if they have a a weapon +2, (or most rings, staffs or wands).
Did I miss or miss-read something?
Are you playing with those guidelines?
I agree that the DM should be a bit circumspect about awarding too much magic armor in particular.
However, these are the guidelines I generally use when determining each higher level PC's starting magic items:
1 common consumable every level from 1 to 5.
1 uncommon consumable every level from 6 to 10.
1 rare consumable every level from 11 to 15.
1 very rare consumable every level from 16 to 19.
1 legendary consumable at level 20.
1 uncommon permanent item at level 4, and another at level 7.
1 rare permanent item at level 10 and another at level 13.
1 very rare permanent item at level 16.
1 legendary permanent item at level 19.
[SBLOCK=What this means in treasure table rolls]One roll on Table A for every level from 1 to 5.
One roll on Table B for every level from 6 to 10.
One roll on Table C for every level from 11 to 15.
One roll on Table D for every level from 16 to 18.
One roll on Table E for levels 19 and 20.
One roll on Table F at level 4 and again at level 7.
One roll on Table G at level 10 and again at level 13.
One roll on Table H at level 16.
One roll on Table I at level 19.[/SBLOCK]
Read more:
http://www.enworld.org/forum/showth...al-quot-Magic-Item-Distribution#ixzz4DWLNm6VT
For example, a 10th level PC might have 2 uncommon items and 1 rare item, and a couple potions/scrolls of common or uncommon rarity.