Agreed on the 75mm L70, the Israelis thought so too with their M50 Super Shermans.
I watched a doco on youtube last night that sort of ties into this, on German tanks-destroyers and assault guns last night. They mentioned the reliability and maintainability issues with the Jagt-Panther. It actually appears the L43 and L48 75mm guns in the STUGs did just fine against the T-34 and Sherman with the 128mm and even the 88mm L71 being overkill.
Very interesting and informative, some minor errors and inaccuracies I picked but overall not bad and got me thinking (yes I know multidirectional, often incoherent tangents again).
The really interesting thread was the majority of purpose designed and adapted tank-destroyers were failures while the simpler, more reliable, Stugs (III & IV), Hetzers and, to a lesser extent due to small numbers Jadtpanzer IV were successful. Basically tactics and employment of the 43 and 48 calibre 75mm gunned Stugs made them infinitely more successful than the other TDs. The guns were perfectly adequate, the tactics made the difference. The monster tanks and tank-destroyers look awesome and I love them to bits, but it appears that, what were in effect, low profile, highly mobile, self propelled, armoured field and anti-tank guns, used in close conjunction with infantry were infinitely more effective than the much fancier, more expensive stuff.