The biggest winner will be Russia, but only if they will manage to win the war. They will get morale boost, Ukrainian territory, people, remaining industry, sea ports etc etc etc.
Russia will no longer win this war, and this is already obvious. As soon as the weather is good for the offensive of heavy equipment and Ukraine receives the military assistance promised from the West, which is already arriving, the Armed Forces of Ukraine will counterattack and in May-June will inflict a residual defeat on Russian troops, and will also liberate almost all of their occupied territories.
Despite the mobilization of more than 300,000 of its citizens since September and the general offensive in eastern Ukraine, Russia has not been able to achieve any success at the front in recent months. Moreover, the largest armored offensive by the Russians near Ugledar turned into a major defeat, where over 130 armored vehicles were destroyed (including 36 tanks), and elite units of the Russian airborne troops were defeated. Moreover, these units never reached the front line and were completely defeated on the way.
Since May last year, Russia has been attacking the city of Bakhmut in eastern Ukraine to no avail. Almost the entire 50,000-strong Wagner PMC and the remnants of the 200,000-strong Russian invasion army in February last year ingloriously perished here. Russia is already running out of military equipment and now rarities from the Second World War are already getting to the front, and Russian troops are increasingly refusing to attack the fortified positions of the defenders of Ukraine. The Russian command has recently chosen the "meat rampart" tactic, when, without artillery preparation and armored vehicle support, it continuously attacks the positions of the Armed Forces of Ukraine in small groups of 10-20 people. Probably in the hope that the barrels of their weapons will overheat in the Ukrainians or the cartridges will run out. Over the past 24 hours alone, more than a hundred attacks by the invaders have been repulsed, and their daily losses on the Ukrainian front often amount to more than a thousand people.
Just to remind you Ukraine has been receiving military equipment from it's allies worth billions of dollars since day one. Why do you think that receiving 30 or 40 German tanks will improve the situation considerably?
As to Bakhmut, from what I've read, is already under siege, it's only a matter of time that it's going to fall. By the way, the attack on Bakhmut started in November not in May as you mentioned. In May some shelling by the Russians took place though. At least that's what Wikipedia has on record. And you didn't mention the Ukrainian losses and they should be pretty severe too.
After such a defeat, Russia is unlikely to remain within its current borders. Five regions of Russia have already held an online referendum for secession from Russia and the formation of independent states. Further it will be even more interesting.
Sounds interesting... Could you please provide a link to your source?