China has not forgotten or forgiven Stalin stiff-arming Mao.
Offensive weapons require lots of training and maintenance. The skilled personnel required to maintain one combat fighter jet? Multiple jets? Replacement parts? Weapons pods? Specialized tools. Look at euro F1 racing team crew numbers. It takes at least thirty fifty people to service and maintain a competitive F1 race car, and no one is shooting at them. And airbases are vulnerable to all sorts of air, sea and land based attacks
The Swedish SAAB built NLaw anti-main tank weapons ruined Russian hopes for a quick end to the land war. Two very large Russian troop transport planes were shot down. Those two planes carried Russia's finest para assault soldiers. They all died. That was during the first few days of the war. One comment upthread noted that Russia sent a lot of untrained kids into battle. It's true. Another interesting feature being Russian military recruited a lot of current and former Chechnya mercenaries and dumped them in the Donbas river basin. They got dead fast - accustomed to picking on unarmed civilians - the Ukrainian militia troops wtfpwnd them. Those Chechnya militia cowards were so used to bossing unarmed civilians they forgot that pissed-off Ukrainian citizen-soldiers might just teach them a end-of-life lesson. This is your Thermopylae. Bravo!