My feeling is that Stage 3 is strong as hell when the hunters have done only the bare minimum, but too weak when the hunters have done well through the match. I guess on some level this means that it’s pretty balanced.
Evolve is a game of trading your resources for the other teams, and so it’s natural that if the hunters outplay the monster at stage 1 and 2 that Stage 3 is basically little more than a hail mary stage, where you’ve been given a lifeline to maybe dig it out of the dirt because you’ve done well enough to get the evolution, but realistically you’d be coming from behind.
Think of Evolve like an (amateur) boxing match, one where the hunters have out boxed you at round 1 and 2. I mean, they beat you to a pulp in round 1 but somehow you stayed standing, and despite good efforts in round 2 they still got much better hits in. In boxing terms you’d have to go for the TKO in round 3 to be able to win, there’s nothing else for it, double or nothing.
The pertinent question about Stage 3 strength is how it is when as a monster you’ve had a tough fight, taking good damage, but also dealing out several strikes. In my opinion, and from my experience, reaching Stage 3 (after evolve) with half your health, up against a team with 3 or 4 strikes, is a pretty fair fight that probably swings just in favour of the monster depending on who has those strikes.
IMO Stage 3 shouldn’t be “Well, I reached stage 3, I win”, it should be “I’m stage 3 now, there’s no more messing around, you fight me, or I destroy the relay”. Hunters survive for long periods during a match because they can split and they can retreat to wait for reinforcements… I feel monsters need to realise that this is their strength at stage 3, making the hunters either remain fighting you against all odds so you can’t kill the relay, or retreating and letting you kill the relay. It puts hunters on the spot like at no point else in the match.