A similar issue happened to me two weeks ago on 1790.

Not all A321s are created equal - the older ones have weaker engines.
Based off of the aircraft specs, runway length and air conditions (heat/altitude), a maximum takeoff weight is assigned.

There are 3 main variables that go into weight requirement - passengers (each adult is assumed to be 150 lbs, each child is less), checked bags (overhead bags are excluded), and fuel. If they are at the limit, they can't carry extra fuel in case they run into a storm without offloading passengers or bags.

There are also different length run-ways at LAS. Two going in one direction, 2 in another, depending on winds. Within the pair, 1 is used for take-off, one is used for landing.

Runway 1L/19R is 8,985 ft long, 1R/19L is 9,775 ft long.
Runway 7L/25R is 14,510 ft long, 7R/25L is 10,526 ft long.

Heat and altitude affect take-off performance. The hotter and thinner the air, the more distance is required to take off.

On my flight - we were originally scheduled to go on 7/25 and it was just about 103 degrees at LAS. We had about 176 out of 183 seats full and started boarding standby passengers. We boarded up to 183 plus a jumpseat. Then the winds changed and it got a little bit hotter (late afternoon, 2pm departure). We were moved to 1/19 and had less space to take off and worst performance during takeoff. We got down to 171 and had to ask for volunteers to take a later flight.

Even with the lighter load, it was a very long take-off and it appeared as the aircraft struggled to gain altitude (although i know the plane did just fine, but part of me was used to 757 takeoffs)

I'm on 1790 again soon (supposedly today but had to reschedule). Let's see how it holds up.