This is correct.

Voldemort was nearly guaranteed to win:

1. He was effectively fighting a revolution/guerilla warfare. He personally had NO weak points (e.g. people he cared about to use as leverage, wealth/posessions to take as leverage etc...).

   His only valuables were Horcruxes that nobody knew about.

2. OTOH, his opponents had multiple leverage points. At the last resort, hostage some Muggles. Or family memnbers.

3. Individually, either Voldemort or his whole group was more magically powerful than any SMALL amount of wizards on opposite side (may be except Dumbledore, but I don't recall good canonical references for comparing the 2 pre-Voldemort's first "death"). So given the low overall numbers of the opponents, with time, they would/could have eliminated them one by one, and avoided the large scale battles if those were not to their advantage (and that last isn't guaranteed anyway).

So, eventually, they'd have won by attrition.

This is correct.

Voldemort was nearly guaranteed to win:

1. He was effectively fighting a revolution/guerilla warfare. He personally had NO weak points (people he cared about to use as leverage, wealth/possessions to take as leverage, etc).

   His only valuables were Horcruxes that nobody knew about.

2. OTOH, his opponents had multiple leverage points. At the last resort, hostage some Muggles. Or family members.

3. Individually, either Voldemort or his whole group was more magically powerful than any SMALL amount of wizards on opposite side (maybe except Dumbledore, but I don’t recall good canonical references for comparing the two before Voldemort’s first “death”). So given the low overall numbers of the opponents, with time, they would/could have eliminated them one by one, and avoided the large scale battles if those were not to their advantage (and that last isn’t guaranteed anyway).

So, eventually, they'd have won by attrition.