They were probably originally intended to counter the T-64/72/80 tanks of the soviet army. But these guys would have been essentially useless anyway since day one. At very best, they might claim to have something near fire power parity with any main battle tank they will conceivably meet. But in every other aspect they would be vastly inferior. They seem imfinitely less well protected, significantly taller and harder to conceal, and less mobile than modern main battle tanks.
In other Words as tank destroyers they would have no advantages of any sort over any tanks they are likely to meet, only huge disadvantages. They would been hopeless death traps for their crew in any engagement starting from the day they were inducted into service.
You are approaching things like this is a game of top trumps, warfare is nothing like that.
These tank destroyers are not meant to compete with MBTs on every level, might as well make MBTs in that case.
The whole point of tank destroyers is that you put a MBT-killing main gun on a much lighter and cheaper chassis, which could be made in far larger numbers and far quicker than MBTs.
These are primarily defensive platforms, intending to hold the line or wait in ambush. Not mount a charge against enemy MBTs over open terrain.
Their light weight means they could go where MBTs cannot, both in terms of open country rural environments as well as bombed out urban population centres. So they make good flanking forces, able to attack the enemy with MBT grade weapons where MBTs should not be able to get to.
These are called tank destroyers, but they are not picky, and will kill anything. In particle terms, unless things goes really bad, these will probably spend as much time killing enemy IFVs and APCs as they do MBTs.
However, the widespread proliferation of man portable ATGMs have started to make these things increasingly obsolete and irrelevant.