I think on a basic level, your mansplainer is probably right - men might have to decide between single or double-breasted suit jacket, 3 or 4 buttons up the sleeve, width of lapels, waistcoat or not - and some of that is dictated by current fashions. But basically, for work purposes, they're probably still deciding whether to go for a dark grey or a navy suit, and if the dress-code is smart casual, it's basically a shirt and trousers.
As a woman, I have the choice of trouser suit or dress suit or skirt suit, or trousers and shirt or trousers and smart non-shirt top or skirt or dress. I mostly wear trousers, for practicality as much as anything, after the day I ended up going under the floor in the datacentre - a skirt really wasn't best for that.
So in terms of acceptable styles available to wear, on a basic level, women do have more choice. But then there are the questions about comparative quality and cost, and also expectations, that you're expected not to wear the same thing every day, or even every week. Women are expected to have a wider wardrobe available to them, so even if a woman's shirt costs the same as a men's shirt, women will probably be expected to have a different range or styles and have more available overall, which means they'll end up spending more.
Then outside of the workplace (and ignoring sports-specific clothing), men basically go from jeans and T-shirt to chinos and shirt to suit. Women's clothing covers a far greater range, according to the formality of the occasion, and the accessories to go with it (shoes, bags, jewellery,) and if you have a summer with a lot of weddings, a man can wear the same suit, but a lot of women wouldn't wear the same dress.
I have at times worn men's clothes in my time - we often had boys' clothes as hand-me-downs when I was a child, but frankly, a t-shirt is a t-shirt, jeans are jeans, a jumper is a jumper. I did get laughed at for wearing hand-me-down jeans when I was about 10, but that's because they were flares, and everyone else had drainpipes by then, not because they were originally boy's trousers.
I wore my boyfriend's shorts in my 20s - I'd been walking to his one summer evening, when I got caught in a short, but very heavy thunderstorm, and I was soaked to the skin when I arrived, even though it was only about 10 minutes. I wore his shorts because they were dry, and my clothes weren't. They were tight on my hips, but fitted. 20 years on, I couldn't wear his clothing, but that's down to me being rather more heavy than I was then. I have bought socks from the men's department, and may well do so in future. I've also bought men's jumpers, as well, and I've had men's shirts in my wardrobe before. But mostly I want clothes which are cut for a women's shape - bigger hips, bigger bust. I'm not just straight up and down.
I've also been to a black-tie do in black-tie, mostly because I couldn't find a dress I liked. I got lots of compliments. I thought then, and still do, that had a man turned up in a dress, he wouldn't have got such a positive reception as I did in a suit and bow-tie. So that is an inequality.
Last summer, one of my male colleagues did comment that I was lucky being able to wear a dress and bare legs (we don't have a strong dress code, but people have only worn shorts in the office on Fridays.) I pointed out that there was nothing actually stopping him from doing so, other than social convention. Pointed out the same when another colleague commented on my bright pink and blue trousers I wore. And they agree - but also point out social convention on some things is quite strong. I just said that someone has to be first. Pretty sure none of my colleagues will be first along that road, though. (We did have one transgender person, but she has since left the company.)
So there certainly are feminist issues around clothing, but it's not half as simple as just having a wider choice of clothes.