Well, I am certainly no expert in WFB, I am still scraping the surface, but I have been aware of WFB for many years, as I did see the models and games while I was into Rogue Trader and 40k 2nd edition. 2nd Edition is pretty cartoony as well, and I played the hell out of it. At the time, I thought the rank blocks I saw in WFB was boring, and many of the models to be kind of silly, like

The collar, sword.

The bright colors. I guess you could paint them however you wanted, but the still come across as cartoony to me. It was one of the major reasons I stayed away. And its not like all the models of this time period were bad. There were some really nice metal minis I still like today. Just the atmosphere I felt they were capturing just didn't work for me.
I felt all that changed when I discovered Mordheim and then the 6th Ed Rulebook. One picture really stuck out to me, and that was the empire troops taking on the River Trolls.
(I tried to post the photo here but the link wont work. Its the one here
https://warhammerfantasy.fandom.com/wiki/River_Trolls with the River Trolls vs the Empire Troops)
It was this single pic that started changing my mind out WFB. I am still amazed by it. I feel the desperation, struggle, violence, darkness, filth, all in one pic, and this feels like the desperate world Warhammer resides in. Or should reside in, to me.
Why does that make a difference to me? I am not sure. Everyone is free to paint minis however they want. But I look to this stuff for inspiration. I have to imagine what its like for those empire soldiers too, and being grounded in some historical sense as far as the look and feel of the armor and equipment, I can imagine the stakes a little more. When I see the stuff in Sigmar, everything looking like its right off the assembly line in perfect condition, its just too far beyond what I feel is realistic and I am not as interested. And I say this about other fantasy settings as well, not just Sigmar.
No amount of literature is going to make me feel how desperate the struggle is when everyone looks perfect. The Empire, to me, was a pretty tough place to live, and I feel the uniforms, equipment, gear, and clothing all should reflect that. Worn so to speak. Used. Sigmar isn't like that. At least not what I have seen.
I do recognize that the Stormcasts are pretty cool in some ways. I feel the masks are great, but not for front line troops. Maybe a bodyguard unit or something. I don't know the lore on who is making all that equipment either, but everything in the old world looks like it was made by a blacksmith, while Sigmar makes me feel its all magical.
So I do look to the art in the books of the time for inspiration, and its what sells me on the mood, no matter what the models are doing. I think GW nailed it out of the park with Mordheim in particular, and 6th that followed. It does seem by 8th things were going a little over the top again, kinda flashy, but still a close derivative to 6th than earlier.
BTW, if I had friends who were old school WFB vets and had 4-5th edition armies, I would do one too for the hell of it.