Width between armrests is only one measure of comfort. At least as important is the width of the armrest/console, and to a lesser extent, the width of the aisle (can matter a lot for a pax in aisle seat in terms of how much they’ll get bumped in the shoulder.

The former is the only readily available measurement. Most (but not all) airlines with 350s do 2-4-2 in PE. I certainly wouldn’t judge DL’s overall product based on that.
UA has 2-4-2 on its 777s and I suspect the seat measurements are very similar to DL’s 350s, prob with the slightly wider aisle.
DL has 2-3-2 on its 330s which is probably marginally better than UA’s 2-3-2 on its 787s.
Both have 2-2-2 on a large fleet of 767s, this is a good configuration for both with no middle seats.