But, unlike frontend devs, designers and product managers believe these complex things are needed, they almost never are and actually bring a lot of issues with them instead. I rarely see a complex component/combination (in a SaaS, let alone on some landing/public page) and think, "well, that adds real value over just a standard component". If you can point some out, please do; there are very obvious cases where something else than standard is needed, but that also depends on your definition of standard; if I can buy complex off the shelve somewhere, you are not building something complex in the frontend and so you can use simple means to hook them up without the complexity.
A lot of custom front end components that I’ve built were more about aesthetics than functionality, so I agree that it’s often unnecessary. In terms of functionality, you can get really far using only native HTML elements.
One common front end component that you can’t build with vanilla HTML is an autocomplete/typeahead input. I’ve had to build a few of these in JavaScript and I do think they’re genuinely helpful. It’s helpful to get suggested options as you’re typing. I also think search results that get filtered in real time as you type are helpful and can’t be accomplished with pure HTML.
But, unlike frontend devs, designers and product managers believe these complex things are needed, they almost never are and actually bring a lot of issues with them instead. I rarely see a complex component/combination (in a SaaS, let alone on some landing/public page) and think, "well, that adds real value over just a standard component". If you can point some out, please do; there are very obvious cases where something else than standard is needed, but that also depends on your definition of standard; if I can buy complex off the shelve somewhere, you are not building something complex in the frontend and so you can use simple means to hook them up without the complexity.