It would certainly help if the financially weaker could devalue their own currency but unfortunately that would necisatate two distinct currencies. Imagine if you introduced a 2 tier system, after a few years the weaker group would devalue producing an exchange rate within the single currency. Imagine the problems that would create. Go on holiday to Greece, spend a couple of weeks there and bring back more than you, d taken. For a two tier system to work,countries would have to revert to their own old currency.
Besides a 2 tier system shows up the stupidity in the initial reasoning behind the Euro. Its a fatally flawed currency for exactly the reasons you justify a two tier system.
How on earth could it ever work with a Euro in Greece being of equal value to one in Germany with their vastly different wealth, living standards, growth and GDP. It can't work,as has been shown in Greece, Spain, Italy and Portugal. Can EU continue essentially what is quantitive easing indefinitely for these nations? I don't think it can, for reasons as I explained in the post about Italy.
I know someone will come back and quote USA as a recommendation for single currency. Its taken USA 150 plus years to get it working, article below is old but explains differences between Euro and dollar..
https://www.thenational.ae/business/one-currency-works-in-us-but-not-in-europe-for-some-good-reasons-1.372370
The Euro is only working because powers that be in Brussels are pumping billions into keeping poorer states viable. That can not and will not last. Either EU must adopt policies as explained in link or simply go back to individual currencies. Problem being the 27 (28?) would never agree to hand over complete fiscal control to Germany (, as quoted in example) or perhaps Brussels. It just won't happen. America has gone through Wars of Independence, Civil War in developing their unified currency and policies making it viable. EU merely thought it a good idea, against opinion of many economists.