Yes, I am a lawyer and I am very familiar with the attorney-client confidentiality of communications. I am also very familiar with the rules that govern attorney-client confidential communications as well as how starkly different the concept of that rule is from the expectation, not requirement, of confidentiality between heads of state when it comes to communications regarding the affairs of their respective countries.
I do see one fundamental similarity though - it’s trust. Be it trust by the clients, or trust by foreign leaders. Can a foreign leader (even an allied one) discuss important things with senior US leadership without them becoming public at will? For any public stuff in leaders talks, there are press secretaries.
One obvious distinction is that when two presidents are discussing foreign policy matters, they are supposed to be doing so in the interests of their countries, not in their personal interests or for personal political gain. It is not and should not be an expectation that in having a conversation that is intended to be a strategic communication by one or both leaders for the purpose of maximizing their country's benefit from working with the other country that communications outside of that scope and go into the realm of potential criminal activity will just be hidden away under the same protections that are supposed to be afforded to them for legitimate purposes.
Legitimate concerns, I agree. However, in that case these tape scripts should be examined, say, in a closed session of a Senate committee, before determining if there is even a small chance of something being illegal. I do understand that political competitors will want to examine to see if there is anything affecting them. That needs to be done though in a responsible way, without any unnecessary publicity that could affect the way President and leadership of the country are doing their jobs - ahead of time at least. Both parties are expected by society to put the interest of the whole nation before those of their party. And obviously, this kind of public demonstration of dirty laundry doesn’t do any good for this country. From outside, it just looks like 2 parties are arguing which of them is crookier and more corrupt - that’s all. Foreign leaders should not get pulled into this bi-partisan competition, and there ought to be an agreement between the parties. Otherwise in 2021 you will be investigating again who elected the next US president - was it Putin, Zelensky or someone else.