I don't know the exact measurement of my bottom step, but I know it is similar in being much taller than the others.

You don't need the extra step. The water creates a buoyancy, so you are easily lifted for any first step. It's not at all the same thing as trying to take that step without water in the pool.

That being said, some people certainly do have shallows steps at the bottom, and it won't hurt you to ad the extra step. But you would definitely be fine without it. So I wouldn't even consider adding it if it juts into the pool in a way that would be inconvenient.

The following section from the 2015 International Swimming Pool and Spa Code might be helpful to you, 809.5 in particular:

SECTION809
SPECIAL FEATURES

809.1 Slides.

Slides shall be installed in accordance with the manufacturer’s instructions.

809.2 Entry and exit.

Pools shall have a means of entry and exit in all shallow areas where the design water depth of the shallow area at the shallowest point exceeds 24 inches (610 mm). Entries and exits shall consist of one or a combination of the following: steps, stairs, ladders, treads, ramps, beach entries, underwater seats, benches, swimouts and other approved designs. The means of entry and exit shall be located on the shallow side of the first slope change.

809.3 Secondary entries and exits.

Where water depth in the deep area of a pool exceeds 5 feet (1524 mm), a means of entry and exit shall be provided in the deep area of the pool.

809.4 Over 30 feet in width.

Pools over 30 feet (9144 mm) in width at the deep area shall have an entry and exit on both sides of the deep area of the pool.

809.5 Pool stairs.

The design and construction of stairs into the shallow end and recessed pool stairs shall conform to Sections 809.5.1 through 809.5.3.

809.5.1 Tread dimension and area.

Treads shall have a minimum unobstructed horizontal depth of 10 inches (254 mm) and a minimum unobstructed surface area of 240 square inches (0.15 m2).

809.5.2 Riser heights.

Risers, other than the top and bottom riser, shall have a uniform height of not greater than 12 inches (305 mm). The top riser height shall be any dimension not exceeding 12 inches (305 mm). The bottom riser height shall be any dimension not exceeding 12 inches (305 mm). The top and bottom riser heights shall not be required to be equal to each other or equal to the uniform riser height. Riser heights shall be measured at the horizontal centerline of the stairs.

809.5.3 Additional steps.

In design water depths exceeding 48 inches (1219 mm), additional steps shall not be required.

809.6 Beach and sloping entries.

The slope of beach and sloping entries used as a pool entrance shall not exceed 1 unit vertical in 7 units horizontal (14-percent slope).

809.7 Steps and sloping entries.

Where steps and benches are used in conjunction with sloping entries, the vertical riser distance shall not exceed 12 inches (305 mm). For steps used in conjunction with sloping entries, the requirements of Section 809.6 shall apply.

809.8 Architectural features.

Surfaces of architectural features shall not be required to comply with the 1 unit vertical in 7 units horizontal (14-percent slope) slope limitation.

809.9 Maximum depth.

The horizontal surface of underwater seats, benches and swimouts shall be not greater than 20 inches (508 mm) below the design waterline.

Step code is correct.

We make our top riser 6" to the rough beam. This to anticipate at least 2" of coping on the beam making the top riser 8"+- which is comfortable. We then calculate the remaining rise the the finished floor and divide the riser heights so there are equal or within reason. The bottom riser can be a little taller than the rest as buoyancy does play a roll. Our treads are a minimum of 14".

The 24" shown, is way too high. It should be split in half.

Yes, steps do take up space in your shallow end. Hopefully your builder was up front about that.

Curious as to what you ended up doing with the last step. Did you add an additional step? Was that the right decision?