It is frankly ridiculous to try to deny that this country's membership of the EU has not involved a progressive loss of our sovereignty i.e. independent control over our political and economic policies. I can only suppose you mistakenly think that because sovereignty to make UK law resides only in our Parliament, and since that Parliament is the only available mechanism to voluntarily make ourselves subject to laws made elsewhere, it means that there is no loss of our sovereignty. It is a wholly circular argument and the tautology just disguises the obvious fact that when we enter any international treaty we become, to a lesser or greater degree, a rule taker rather than a rule maker. Brexit has always been about sovereignty
as defined in its widest sense - a debate to decide who has the final say in following our national interests and to what extent they are under UK democratic control.