Okay lets talk ground game since no one has debunked Stellaris Common Wealth being more than able to compete with every existing faction.
Federation troops will have their forces in addition to being able to recruit from the Common Wealths 750 trillion population per OP. This gives them a nice reserve of troops which will be further supplemented with lost or abandoned former Imperium colonies being absorbed and relocated to safer territory.
Now Federation troop Morita is the standard rifle so if they're planning on not destroying everything they'll be using this.
Gauss Tech 7.62 rifles not bad, they're also noted to be accurate over 1,000 meters so more than triple an AK-47.
This effective range would allow the bog standard trooper to compete with Tau at range
Testament to the Morita Gauss Rifle speed and power .
MK II Morita uses grenade launchers with wide shrapnel radius, excellent for slaughtering Eldars who rely on holofields. Oh you're not really there? Too bad I just shrapneled the entire area with in tens of meters.
Armor? Meet Federation phosphorus that burns with the heat of a thousand suns, plasma weapons be coping at the bullshittery
Marauder no selling triple digit gigajoules worth of thermal energy, bullshit incendiary/thermal weapons are bullshit.
The Guardsmen will piss themselves when they see this beast shrug off Las Cannons.
Armor piercing 15.5 mm Vulcan rotary cannon , so Anti-Tank rifle minigun 😬 then you have the 155mm Howitzer.
This is only scratching the surface and its already enough to make the Tyranids flee in terror.