The 75mm could sometimes penetrate the Tiger frontally, but not even the 76mm gun would do it reliably(Yes the 76mm would, the panther not as likely due to the sloped glacis, but thanks to flat armor, the tiger would be screwed). Reliably implies most hits resulted in pens. We have all seen pictures of German tanks scarred by multiple shell ricochets (don't remember any similar Sherman pictures by the way)(If you dig enough you'll find a situation where just about any tank bounced a lot of shots. Hell, stuarts bounced a lot of shots from jap tanks in the Philippines, that doesnt make the stuart some pinnacle of armor layout). Other than the mechanical reliability question, how did the Tiger fail as an assault tank? It has more armour and a more powerful gun than the Sherman or T-34. Obviously not invincible but better than anything being produced by the allies in 1942 when it came out.
(KV-1E says hi. More armor than a Tiger and sooner to boot. Neither the M4 nor the T-34 are really assault/breakthrough tanks, they're mediums. With the exception of specialized variants like the Jumbo, they weren't meant to be line breaking tanks, this is extra true in the T-34's case, since the soviets deployed several heavy tank models throughout the war to fulfill the assault role, and most were better than the Tiger. Also, the Tiger's frontal armour isn't significantly better than an M4's as far as effectiveness goes.)
Panther was even better with similar armour protection, better Anti-tank performance for its gun, and better mobility than the Sherman(Except reliability that almost makes WW1 tanks look good... Also, it's armor protection was garbage for a tank of its size, literally the only strong spot was the glacis, otherwise the turret was meh and the side got penetrated by archaic anti tank rifles. A 45 ton tank, beaten by a 14.5mm ATR. If that isn't bad, I don't know what is. Also, yes, it's AT performance was good, while its HE performance really wasnt, which is important for a tank to root out infantry, finally, its mobility is highly overrated since it assumes perfect conditions and an engine at ungoverned output, in practice the output was something like 560 vs the advertised 700hp, which meant the Panther wasn't as well engined as people seem to think, much less the Tiger/KT)
How would an equal number of Shermans be a more dangerous assault force than Tigers or Panthers? Admittedly Tigers and Panthers do no have a long record of success on the assault because by the time they were available in meaningful numbers the tide of war had already turned(No, they have a record of failure because they couldn't do their job. The Panther's at Arracourt outnumbered their opposition, much of which was basic M4's, and they still got trashed. Also, infantry/defending tanks doesn't particularly concern itself with your armor, especially when its as bad on the sides like a Panther, thus engagement/response time was far more important. Due to a bad gunner sight system, the Panthers response time was far worse than an M4's. The Tiger might have been better in that respect, though I'm not sure. It's turret traverse is well known to be garbage though. When I think of Panther/Tiger vs Sherman engagements, I think of the early DDay counterattacks, Villers Bocage, Wittmans deathride, and Arracourt. Of those, only Villers Bocage was debatably a draw thanks to wittmans solo ambush, even though Wittman lost a large chunk of his command to everything from 6pdrs to Firefly's, as well as losing his own tank).
The German military lacked the logistics, air superiority, and fresh troops to support offensive operations. That was the reality on the ground. Not anything the Tiger or Panther can directly be faulted with(None of which was relevant during Wittmans death ride, Arracourt or Villers Bocage).
On a one to one basis the Tiger and Panther were powerful opponents(War is not one vs one, and if I want a one vs one slugfest tank in their weight category, the IS-2 is superior in almost every way that matters, thanks to the lack of tank reliability and numbers, common German infantrymen were left out to die without armor support, the M4 could be just about everywhere. Also, neither tank had a significant enough advantage anywhere except in a 1k meter bowling lane, which isn't how real war is fought, especially not on the Western Front, shoot first hit first are the most important aspects, and especially in M4 vs Panther, the M4 is far superior).
The allied strategy of mass producing of a tidal wave of simple, reliable, adequate tanks like the Sherman and T-34 was a war winner, but we still have to admit the technical quality of the German tanks(What quality? They introduced nothing novel in their tanks, suffered horrific breakdowns, were terribly armed and armored considering their weight and often had absolutely crippling deficiencies like the Panthers engagement time. There's a reason few if any of the technical innovations introduced on later war german tanks were used post war, and that's simply because they weren't that good. Literally the only major advantage, kinda, I can think of is their suspension, which reportedly gave a very smooth ride/accuracy on the move, although the M4's stabilizer probably compensated somewhat, of course its maintenance issues are well known though).
The Sherman and T-34 were good tanks. The Tiger and Panther were better though and there is no shame in admitting that.
Better in what? Their performance in combat wasn't better, especially not in the West. I simply don't know enough about the general combat in the East(not one off incidents like 1 T-34/85 KOing 3 KT's or whatever) They're only better based on paper stats. Their ergonomics weren't really better, their availability wasn't better, the Tigers armor wasn't really better and post 1943 even their firepower wasn't better, and this is all compared to 30-35 ton tanks. The moment the Panther/Tiger is compared to an IS-2, let alone an IS-2 M1944, it is a total disgrace. They were better than the allied medium tanks in one situation. Frontally engaging tanks of a 10-25 ton lighter weight class at long range. Unfortunately, if you wan't a vehicle to do that job, you have the JpzIV, same gun, far better concealment, similar armor(at least adequate to ward of a standard M4 shot)