Anti-Vehicle infantry are too effective against other infantry
A blob of Lascannon devastators has enough dps to substitute for any kind of dedicated anti-infantry in a Space Marine army by the end of a match, with the added benefit of being effective against all armor. The counterplay to AV infantry should be melee infantry, but it's extremely difficult to shut down a SM blob using infantry because if they reach a critical mass they have enough DPS to destroy a charging squad before it does any considerable damage to them. This problem becomes more exaggerated in the late game, as the way that infantry armor/shield upgrades scale means that infantry units take longer to kill.
Suggestion: Lock focused anti-vehicle weapons (weapons that increase in DPS over time against a certain target) to their base DPS against targets that do not have Heavy Armour.
No early-game counterplay to Flamers
Flamers have extremely high DPS and can melt an early-game army in seconds. They come with a significant power cost, which is justified, but what isn't justified is the fact taht there's very little that can be done about a flamer squad in the early game.
Suggestion: Make the Tactical Marine flamer a channeled ability just like Kill Team Ironmaw's, meaning that it stops functioning if it is silenced or engaged in melee. Consider lowering the DPS and power cost slightly.
Racial global abilities scaling in to the late game
Something also suggested in another thread very recently. Space Marines global abilities scale in to the late game (they also have no resource costs whatsoever). With every tech level, they get an extra drop pod, and their banner gets new effects, giving them extra offensive abilities in the late game. I don't play Orks, but for Eldar there is no similar effect. This means that their global abilities get weaker over time rather than stronger. Indeed, it actually gets harder to fight within webway range in the late game. This is because battles are less focused over resource points, and will move around the map. Webway gates can also be destroyed in seconds by most armies, putting the Eldar at a huge disadvantage.
Suggestion: Make Webway gate Fleet of foot effect radius increase with escalation phases, such that by escalation phase 4 it is much easier for Eldar to use webway coverage as an offensive tool. Realistically no Eldar player is going to make more than perhaps 4-5 webway gates in a game, and this should be enough to cover most of the map.
Also consider: giving webway gates a passive Stealth ability in tech 3, and passive armour regeneration out of combat in tech 2, but also increasing their power cost at later tech levels, perhaps up to 50 power each in tech 3, so that the Eldar player is rewarded for using the early game to establish webway coverage in to the future, rather than building them in their base and relocating them when they make an assault.
Some inconsistencies with upgrades
The Eldar have to purchase upgrades to buy some of their own units, which to my friends who play the other races is laughable. It would be more logical for Shadow Spectres to be a T2 unlock, but to remove the warrior portal upgrade completely, so they would be equivalent to Lascannons and Tankbustas.
Many Eldar units are unable to fulfill their potential without Soul Shrine upgrades; the issue with this is that by the time the upgrades have been researched, the game has moved on and these units are no longer useful. Quick Strike is a particular problem here; since it's damage has been reduced to being negligible, it's only useful as a hard counter to Heavy Weapons Teams in shield generators/cover; this is such a niche use case that I might only get it use it efficaciously once or twice per match; but if I did spend the (50!) power on this upgrade, given that it takes at least a couple of minutes, that opportunity is likely to have passed me by.
Suggestion: Alter Taldeer's command doctrine so that it enables the ability without purchasing the upgrade. Also consider: Simply making it available to Banshees by default. It's a pretty weak move as it is, and Assault Marines get a jetpack, while also being the best unit in terms of health and DPS in t1, so why would you not give Banshees a similar ability to close the gap?
I hope these suggestions are constructive. As MrBenis points out, one of the issues with this game, and with the Eldar faction in particular, is that many of their abilities have been 'pre-nerfed'; designed to be useful, and then watered down to the point of being useless. Space Marines for some reason have been excluded from this, and they are the most powerful faction as a result. This means that the solutions to a lot of the problems which the game has are very simple, and are just a logical extension of mechanics already in the game. I hope these issues are ironed out quickly, as I think this game is very unique, amazing fun and has a lot of potential; balance issues, however, have to be dealt with first and foremost.