Sort of, but since the aisle seats are angled, principles of geometry would dictate that achieving 1.5" of width reduction across the horizontal axis of the airplane would require slightly less than 1.5" width of the seat cushion as the passenger is oriented. It would be true of the window/center seats, though.

There's only a finite amount of space in the cabin, and with a similar density, something has to give. My guess is the Delta footwells will be much deeper than United's, and the wall in front of the passenger (containing literature pocket, TV monitor) will be closer to the passenger than Polaris. There also will be a similar lack of storage space.

Delta's seat may indeed be more spacious than Polaris, but we aren't talking about the SQ Suites here. One thing I find is that United was attempting to strike a balance between a business class seat that resembles a private cocoon with a desire for a more open cabin concept. After market research, I don't think there was a clear winner of one over the over and enough passengers felt strongly enough about their respective preference that United felt it important to attempt to accommodate both.

After sampling the center and aisle seats, I found them as private as any business class product in full recline (around the head/shoulder area), but in a more upright position, you don't lose much of the openness of the cabin. I like that. The center seats will be pleasant for traveling as a couple, while at the same time preferable to the Solstys "honeymoon" seats in service with airlines like AB, AZ, EY, OZ etc., which cant slightly toward each other and do not have the same privacy divider as the UA Polaris spec. Finally, the window seats will be great for solo travelers, but I do not think the outboard armrest will be especially comfortable.