So let's say they go through with your nerfs.
He has a base HP of 784 health at level 4. And a base regen of 9.7 per/5 seconds. With a Doran's shield that jumps to 15.7 per/5 and an additional 13 per5 with passive (1.5% of 864) makes it come out to 28.7 per 5 or 5.7 health a second, 864 for HP with Doran's. 864/40 Means he can use it for about 20 seconds before it runs out. Flipping it around it takes him 151 seconds to regain full health. W is taking away his HP by 40 a second which is 8 times his regeneration at that level. While he's engaged on someone- and each axe he throws is 50 health; meaning it takes off 1 second from that 20 if he doesn't hit the target, and takes a little over half a second of possible health that could have gone towards burning agony, in this scenario we're saying he put 3 points in W with his Q a single point. He's basically throwing his health away the entire fight during those times. Even if he got more HP your scenario makes him sacrifice a lot of health/damage simply because you do not like how he is. It takes him completely out of the fight at times when he trades poorly and against range I'd argue he's at a horrible disadvantage, his attacks consist of a single skillshot and having to stand on top of you to even use the ability you're talking about.
I think Mundo should be fine tuned but this ^ definitely doesn't help anything and takes away a large portion of his engage/sustain simply because you don't want to play around it from the looks of it.
"I hate people building this dude tanky and maxing out his W"
I've never seen someone max out their w, nor have I ever done so on Mundo unless it's a pure on engage and I'm ahead with items. At that point it's like any other champion- they have items over you, unless they slip up you need to play around their strengths. Heck I'd argue NEVER maxing W first, E is far more useful. In fact I'm pretty sure W is LAST on people's list going Q>E>R>W because E gives you way more pushing power and overall strength in duels, which is what he excels in and you seem to have a complaint about?