A BVR fired from high altitude has a lot of potential energy and will be able to cover a lot of extra distance when mixed with both Kinetic and potential energy. Speed will be significantly less though. So, a missile at Mach 4 fired from high altitudes may reduce to Mach 2 at lower altitudes.
While advertised figures are a benchmark for different missiles, the advertised figures can be exceeded using superior platforms firing it. A R-77 fired by a fifth gen Aircraft will be far superior in kinetic energy compared to a R-77 fired from a MKI and so on. So, advertised figures are figures that are achieved when fired from subsonic speeds at medium to high altitude.
So, if you take a R-77 fired from 10000m and Mach 1.7, the missiles will far outrange the same missile fired from 1000m and Mach 0.8... and so on. Large air superiority fighters also have multiple altitudes and speeds compared to small fighters too. So, this gives the pilot more options in using tactics and achieving a better firing position.
Long range missiles like Aim-120D/RVV-BD/Aim-54 and Meteor work differently. Meteor claims similar ranges to current BVR missiles, but almost all of the flight is "powered" because of RAMJET propulsion and the speed does not reduce drastically due to air resistance. At long ranges modern conventional missiles follow a ballistic path to extend range. In this mode the missile has a higher potential energy and develops more kinetic energy as it travels towards gravity. Something similar when a BVR is fired from a high altitude to a target at a low altitude. You can say it is lobbed towards the target, the missile flies at very high altitudes, like 100000 feet when we are talking about Aim-54, no idea about others.
So, advertised figures change based on how the missile is used. You can even use missiles in dog fights. For eg: If we assume you cannot use your radar for some reason, you can use the missile seekers to lock on to the target before launch at ranges of 10-18Km on R-77. This is what Mig-21Bisons did against F-15s during CI-2004.
You can say advertised figures are mostly useless if you want to compare. A missile like a Aim-120C7 which claims to do 110Km will actually do near 160Km if fired from a high altitude. In practical situations pilots prefer firing their missiles from much smaller distances.
In relation to 5th gen aircraft, none of the above is possible against it because of low detection and tracking range. So, you can't lob a RVV-BD, when you can't see it. At closer ranges you will have a take a more direct heading instead and this reduces capability of the missile as compared to the ballistic path.
Opening weapons bays only provide detection and only for a very short interval, like 1 to 2 seconds. If you fire a missile at the target on detection then you are firing your missile blind. It is not a useful shot. You can use it as a tactical shot to keep the enemy occupied though, but only if you have enough number of missiles on you, that's why the need to have 6, 8, 10 or 12 BVR missiles on the aircraft. Lock is achieved only when the pilot is sure that he can fire the missile because all modern aircraft have indicators that warn about radar locks. So, before lock you need to track the target, that's not easy at all.
Detection is just a blip on the radar screen. It does not give any information.
Track is when you can follow that blip consistently. A lot of information is received and as the tracking signals provide more information you are even able to identify the target. Different modes generate different information signals like the harmonics from the compressor face of engines or the number of weapons carried along with the type. Radar can count the number of blades an aircraft has to identify what type the aircraft is. Detection is not enough to give this information.
Radar Lock is when you are ready to fire the BVR missile.
A detection in no way means a track, let alone a radar lock.
Not true. Or partially true. It is true that a 4th gen aircraft is cheaper and easier to make. But modern warfare is no longer about getting cheap things into the battlefield anymore, like it was in the past. There is a concerted effort by all countries to get the best of what's available into their forces regardless of how much it costs. Some countries are not so lucky, but some are. Countering the lucky ones like China is IAF's priority.
The kind of thinking where people believe they can afford 4 LCAs to the price of 1 fifth gen Aircraft is regressive and dangerous. Let's say the fifth gen Aircraft can always take out three LCAs but is always shot by the fourth LCA. Will you as a Commande accept it? Three of your pilots are dead, now what? Tomorrow 3 more pilots will join with 3 more LCAs, they will die while you take out the fifth gen Aircraft. This will go on and on. In the end your side lost 3 pilots to the cost of 1 enemy pilot. Or 300 pilots to the cost of 100 fifth gen Aircraft. In terms of statistics the material loss wa similar, 3 LCAs for 1 fifth gen Aircraft. Acceptable?
How's this as an example of the changes undergoing today?
Interview with Victor Mikhailovich Chepkin - Vayu Sena
A lot of gyan here.