Hello! I am a big fan of your game.
However, as you may have noticed... many players have been posting thread forums titled:
Space Marine 2 difficulties are bad
Melee classes feel very underpowered compared to Ranged
Many weapons feel underpowered

So on and so forth. There are more than the above but you'll see a trend.
Many players are complaining that around difficulty 3 (Substantial) and difficulty 4 (Ruthless) enemies feel 'bullet spongey' (words the PR of the dev team used in your last Q&A I do believe).

I think here what we have is a matter of philosophy to the approach of what makes something 'hard.' Sure you can scale something's health and damage up 500% (or whatever it is), but this isnt rewarding or 'fun' for players. Players want to feel the power of their wargear tearing through countless nids, they want to feel the visceral reward of every kill. More killing = more power = more fun. They also want to feel challenged from the enemy behaviors of those that stand out from the swarm (i think the lictor and ravenor both have fantastic behaviors. They are extremely menacing and accomplish their role well. Though I do wish the lictor wall-crawled more.) Enemy behaviors and enemy quantity provide a more skill based and rewarding challenge to players rather than >>>shooting a warrior brood standing in place, a ridiculous number of times to get it to incapacitate. Or having to shoot a mere gaunt 7+ times with a fully fledged bolter.<< This is why in order to make the game 'fun' you need to not mindlessly scale up health and damage but instead scale up the QUANTITY AND DIVERSITY AND BEHAVIORS OF ENEMIES. This is what would make players have more 'fun.'
1. Scaling up enemy quantity permits players to retain their sense of power as they massacre their way through enemies but the danger is still in getting overwhelmed (lore friendly)
2. I would look to see more Terminus aka Boss enemies making their way into horde/swarms instead of spawning solo. (this is also, more lore friendly) Carnifexes.
3. I would like to see 'patrols' of enemies moving through the map. I dont feel like packs of enemies standing in place feels very 'alive' in terms of a swarm assaulting an imperial world... It completely breaks the immersion for me. There should be a SIGNFICANTLY larger alert radius for what packs pull on higher difficulties, and the enemy presence and map control needs to be felt by players. 
4. Tyranid swarms need more enemy diversity. More body. I would personally very much like to see adding ripper swarms (a writhing mass on the ground with a hitbox like anything else). Per the lore, zoanthropes, neurothropes, and other psychic creatures heavily accrue huge swarms of rippers, so I would like to see rippers incorporated into encounters with psychic nids. 
6. Warrior Primes (just a larger warrior equipped with all their weapon types usually) would also add a daunting challenge standing amidst a pack of warrior brood. The model is also mostly already there you just make it bigger and add some variation. It would be really cool if warrior's altered their behaviors whilst in the presence of a warrior prime as well. 
7. Increase player squad size to 4.
8. Chaos is just not fun to fight presently, i'm here to kill bugs. 
I understand these asks are a larger demand for your server scaling. But I believe you have a successful game on your hands (if the sales are to be believed) and investing in your own product will reap you a greater long term reward.