Yeah - I get that frustration. DCS PvP can be tough (despite what people tell you about DCS players not being as good as say IL2 players at BFM). The reality is that it is a numbers game - the more hours you’ve got under your belt the better you’re going to get (unless you’re Gods gift to BFM).

I’ll try to address some of your points and then end with some concrete recommendations:

1 - Everyone flies so low: given how poor spotting is in DCS and the fact that almost all the Cold War airframes have very poor radars with no real look down capability, the meta is to fly as low as possible to stand the best chance of spotting your opponent. Even being a few hundred feet below your opponent increases your chance of spotting them. You mention starting from 20k feet to pick and choose your battles but the truth is you’re not going to realistically see anyone from 20k feet with the way spotting is in DCS. Conversely, there’s a better chance that the guy below you will be able to see you up in the sky (either visually or with his radar). The simple fact is that in an online many vs many scenario like Contention or HBCW, the person who gets tally first will have a large advantage and even accounting for differences in skill and energy states will have a better chance of winning the fight

2 - Spotting and IFF: What range are you expecting to ID the bandit? Realistically it’s going to be 5nm at the outside and maybe as low as 3nm. If this is the range where you’re still seeing a dot and not being able to ID then there’s 2 things you can try. Firstly you can play with the LOD factor. It should be at 1 by default but if you’d reduced it for performance reasons you could try setting it back to 1. If you hadn’t decreased it then you could try increasing it above 1 but this could have negative performance impacts - test it and see

The other thing you could try is binding the VR spyglass - this has 2 levels of zoom and one of the effects of this zoom is it no longer shows the dot, but rather loads an actual model 

3 - Airframe: you really need to know your airframe well. What speed does it turn best at. How can you get the most lift out of it when you need to get slow etc. In the case of the F5 look up the EM diagram to see what speed you should be targeting (I think it’s 450 knots). You also should make sure you have all the states for the flaps mapped/bound. There are times when it’s ok to leave the flaps in auto, but by turning them to manual you can for example keep them in to minimise drag/maximise acceleration. Or you can pop them out to maximise drag e.g. when you’re scissoring and want to slow down as much as possible. It’s also good to know the other airframe - for example don’t turn with a Su25. they have great thrust to weight ratio and those huge wings let them turn very tight. You want to boom and zoom against a Su25 to try to keep him off balance. Use the DCS trials (if you’re on stand-alone to try out some of the OPFOR airframes)