Please don't repeat that again, we have discussed that extensively in this and another threads. It is simply wrong that it can be "fixed" (at least not easily, BTC would have to adopt the Monero or Grin protocol to "fix" it).
Let's first define the exploit and the problem then see if it can be fixed or not.
The exploit is that the Bitcoin protocol previously had strict rules about stack item sizes and script sizes. These rules were loosened for witnesses and that means the attackers can now inject an arbitrary size data in their witness without the tx becoming invalid.
This can and should be fixed.
What you are explaining is another attack vector that had existed from day one and was also exploited in early days leading to introduction of OP_RETURN rules and said "exploits" were moved into said output types.
As I've said before, in a decentralized blockchain we can not prevent abuse. What we can do is to make it harder and more expensive. For example we could never make a spam attack impossible (like the so called "stress test" pre-2017) but with fee market we can make it harder and more expensive.