Corroded wire, tinned or bare, will have a high resistance than non corroded wire of either construction.
There is nothing inherently wrong with non tinned wire.
Having corroded connections that have not been serviced is the problem. Not the lack of tinning.
Is tinned wire better for corrosion control? Yes!
Does it guarantee you will never have connection problems? No!
The ECM is not going to be damaged by low voltage. That happens every time you turn the engine Off.
When a bad connection causes an intermittent disconnect of the Battery;
The voltage regulator in the Alternator can spike to over 100 volts, killing the ECM.
Could a corroded NON Tinned wire possibly damage an ECM? Yes!
Could a corroded TINNED Wire possibly damage an ECM? Yes! Again!
Don't blame the wire! Blame the lack of preventative maintenance.