Why do I think Russia is winning? Mainly because it has artillery superiority. The Ukrainian-reported daily losses of Russian equipment show that Ukraine isn't able to dent the artillery much:
For the past week, it's 21 artillery pieces. Average of only three per day, and it's been in that ballpark for past months. This is out of estimated 3700 or so that are in Russian arsenal before the war, not counting ones being produced or repaired currently.
This pace is not good enough. For comparison, Ukraine has been given about 350 western 155mm artillery pieces, of which about one third is reported to be out of action; destroyed or under maintenance. I think Ukraine needs to step up its artillery game with more accurate shells (I hear GPS guided Excalibur shells have done a great job, but of course they cost 100 or 1000 times what regular shells do), UAVs, and ways to destroy Russian jamming devices and such, counter-battery radars, and simply having faster turnaround time from observing the enemy to firing at their position. Russians are still better at this.