R-77M is more important for su-30/35 that aren't stealthy and lack first shoot capability against aim-120D or meteor equiped western aircraft or pl-15/21 equiped chinese aircraft. R-37M isn't a replacement for r-77-1 even if it allows them to shoot first.
The R-37M can engage targets pulling 8g and is intended for use against fighters as well as large aircraft and cruise missiles.
R-37M is not a replacement for R-77-1 but it can do the job till newer missiles are ready... targets being shot down at 200km plus ranges in Ukraine suggests it is being used and we have seen photos of them being armed with such missiles.
This things work both direction.
Sure you can make a missile that will fly 3km/s, yet it will struggle with accuracy for the very same reason.
A scramjet engine means they can approach the targets at any speed they please... the enormous speed of the missile basically equates to effectively making the target move in slow motion in comparison... as the missile approaches the distance the target can move and the directions they can go is minimised by the high speed of the approaching weapon... if the target is flying high where the air is relatively thin detonating the warhead early spreads fragments over a wide area with speeds that would cut through anything... equally on their major SAMs they had smart fused warheads where the targets location was determined at the last nano second and the appropriate detonator initiated on the opposite side of the warhead from the projected location of the target so the explosive essentially blew the fragments of the warhead in the direction of where the target will be when the fragments arrived... but considering the missiles flight speed a tiny HE core charge as a column in the centre of a cylinder of metal fragments stacked in the warhead section where the HE just acts as a spreading charge to blow the fragments out in a dense pattern nano seconds before impact to create a hypersonic shot gun blast...
Some of their faster missiles had side thruster rockets that operate for a split second and are located around the missiles centre of gravity so when fired they don't turn the missile... they shift the missile sideways a metre or two to ensure missile to missile contact (used for very small targets that are hard to hit no matter what the speed).
In 2 minutes the enemy has enough time to go low between mountains and evade your missiles.
Do they know it is coming and who it is coming for... but more importantly a very long range missile climbs to high altitude... think about enormous altitudes... like a satellite taking photos of the ground... how effective would flying very low in mountains be in evading a missile coming down nearly vertically?
I agree if the missile was ground launched and to hit you the launcher had to track your target then mountains are a perfect idea to cut the signal and the view, but a lofted missile with active radar homing (ie its own sensor) then flying very low in mountains just means you slow down a big and you burn more fuel.
Higher speed gives you also advantage even if your opponent has same or longer range missiles.
Plus the high efficiency of a scramjet engine means you could launch a Zircon sized missile where the several hundred kgs of HE and the jammers and radar sensors could be replaced by Verba or other small missiles... released from 30km altitude directly above a group of enemy fighter aircraft, some sort of Main IR sensor on the core missile detects targets as it starts to descend and by datalink allocates a specific target to each of the say... 10 or 15 light compact missiles on board the carrier missiles which will then individually guide to target aircraft, or any cruise missiles they might have already launched... the missiles could dive and only light up their own rocket motors if they need to manouver a bit...