This 3 : 1 ratio of troops is so fucking stupid. Or rather how they apply it. And i'm not talking about:
>the attacker always suffers 3 losses for every 1 defender
situation, but when calculating necessary troops, because they think 3 times more troops needed for the hope to succeed. So some might suggest that 250K Ukrainian troops can hold up to 750K Russian forces just fine.
There is even a US recommendation to hold 1 km of frontline with 250 troops. So that 250K can be comfortably spread out along the whole 1000 kms of frontline.
But let's say the Russians only send 250K troops to the front to face the AFU's same amount. Then they take only 1 soldiers from every km - gaining 1000 free soldiers to place -, and concentrate them to one specific km of the front. There they can achieve a 5:1 ratio of majority with pitching 1249 troops against 250.
What if they take 2 soldiers from every 250? What if they take 50?

In WWII the balance of Germany vs France when the former invaded the latter was this:
141 divisions vs 135 divisions
3,3M troops vs 3.3M troops
2445 tanks vs ~3500 tanks
5638 aircrafts vs ~2900 aircrafts
Considering it's about an 1:1 match the Germans did brilliantly. Why? It wasn't about the full sizes, but how to concentrate them.
Data is taken from Wikipee for I was lazy: https://en.wikipedia.org/wiki/Operation_Barbarossa

So pulling troop numbers out of someon's ass, based on the 3:1 ratio is nonsensical.