With four bathrooms already in the house, I would not force a tub into this master if it makes the shower feel cramped every day. For most buyers and for daily use, one good shower in the primary bath is usually more valuable than squeezing in a tub that steals comfort and circulation. Since the kids' bath already has a tub, you are still covering the practical resale question.

If you keep the larger shower, I would spend the planning effort on clear glass dimensions, niche placement, bench depth if wanted, and where the vanity, mirror, and lighting will land so the room feels intentional rather than crowded. In a primary bath, those proportion decisions usually matter more than checking the box for another tub.

I work with a lighting and metal hardware manufacturer, so I look at this from a production and QC perspective. If you compare both layouts, pay attention to true walk-in shower width, door swing clearance, and whether the mirror or medicine-cabinet wall still has enough usable width after plumbing and storage are set.

At a certain level of house, amenities contribute to it's value whether you personally use them or not. Yeah, people like to say "build it for you, not the next person," then complain when that time comes and it is a detriment because it does not hover around the "median line" of design attributes that are an expectation in certain houses. Not always, but usually a 4000sf house might mean a certain level of quality, amenities, and comparables.

The portion of plan does not indicate enough of the house to understand if a Master tub is expected, and there are some unknowns (like where did the Master door get moved to?). Also, the layouts for each scheme are not the best, each has improvement to be made, which may mean that if having a tub in this house is important enough, a design can be schemed that may work better than these.

Larger shower and no tub for sure. One tub in the house will be fine even if resale value takes a (slight) hit.

I’d probably test both versions at the exact dimensions before giving up shower space for the tub. On paper a few inches can look insignificant, but in a shower or the walkway between fixtures they can make a big difference.

You could recreate the bathroom and try both layouts in this free 2D/3D planner:

https://homdera.com/en/tools/home-planner

I’d compare the shower width, door clearance and space around the vanity in 3D. With another tub already in the house, I wouldn’t squeeze one into the primary bath unless the layout still feels comfortable.

There are probably better configurations for the bathroom. Adding a tub wouldn't be a necessity for the vast majority of my custom home clients--who tend to prefer a larger, more elegant and functional shower to a shower and tub. Ditto for my remodeling clients--the majority of whom ask us to eliminate the tub when remodeling their master bathrooms.

How long will you be in this house? Will you be selling at some point. I tub in a master bath is very common in our designs. We very seldom have primary bathrooms with no tub and a shower only. Am thinking any future buyers will be expecting there to be a tub in the primary.