Q1: Is this a major event? I don't understand why the media even bothers reporting this.
This might look too harsh (so please help me to edit this), but this is probably because you have very little understanding of military and war.
Death of a general is extremely important even by itself. Those are not the people who are on the front line and engage in a fight. They should not be killed at all so yes, this is a very major event. Those people are responsible for general strategy and have information from various subordinates (who usually do not share it between each other). If you worked at any decently sided organization working on any more or less complex problem, you should know how much time it takes to onboard a new lo-level manager (for example in Fb/G it might take half a year). Now imagine how much secret information a general should know about different parts of a front. You need to find a suitable person:
- whom you can share all this information
- who will be able to comprehend all it in a timely manner
- whom colonels will trust and support
- who has expertise in that area and is not doing anything useful now
In many more or less complex organization there is politics involved and in Russian army this is even more so. So with the death of high-level guy there is a lot of uncertainty. One of those colonels/colonel-lieutenants might have relied on old guy for their promotion/better treatment so they are not enthusiastic with that option disappeared. Some were against it so now they have an option to show how bad the old guy was. This creates more tension and anarchy.
Now your point: oh they have 1300 generals. Generals are not a commodity (basic goods interchangeable with other goods of the same type). You can't easily substitute one for another. To give you another example from business: lets assume that one of the CEOs of big US companies have been killed (suddenly killed, not died months after he officially resigned and years after his serious illness was known and another guy was already taken his responsibilities). Based on your point "what's the big deal, US has thousands of other CEOs", but I can guarantee you that market will react to this very swiftly (with stock tanking), people inside the company will react also with interviewing for another companies.
Q2: Is there any correlation between a general being killed and subsequent problems for Russia on the battlefield?
First this is usually a delayed effect. In the beginning situation is becoming bad and high-level guys have to react to this. They are moving closer to the action and get killed (that guy was killed on a mine). As I told in a previous question, this should not even happen.
Now regarding a problem on the battlefield. This is 645th day of the '3-days fast military operation' of the '2nd best army in the world'. Army whos active personnel was 5x bigger, had 5x more APV, 10x more planes and helicopters and having 10x more budget and infinitely times more navy.
If loss of 330k people, 300 planes, 300 helicopters, 5k tank, 10k apv, 22 ships is not showing problems on the battlefield, then I am not sure what will you count as a problem.