Is Ukraine becoming the sacrificial lamb?
Yes, but perhaps not in the way you mean.
I think that the sanctions and military support were never intended to protect Ukraine, but to prevent Russia from
trying this with other counties in the future, by making them pay a very high price for Ukraine.
My view is based on two assumptions;
1 - There is no realistic chance of Ukraine winning. The only way this ends with an independent Ukraine is if Putin backs down.
2 - Putin has put himself into a position where he can't back down.
If these assumptions are true (and I think most people agree that they are) Ukraine does not benefit at all from this outpouring of support.
In fact the more support they get, the longer the battle, the more Ukrainians die, the more of Ukraine gets destroyed, and the end result (a Russian controlled Ukraine) is otherwise the same.
For the rest of the world however, the longer it takes and the higher the price Russia pays, the more likely that they don't do this to anyone else.