I figured peoples beef with the stormcloaks was their
- Racism
- Ulfric being power hungry
- Not being as strong as the empire regards fighting the aldmeri
Stormcloak Racism
The stormcloaks seems to be very racist against the dark elves so i investigated windhelm , stormcloak HQ , so yeah they live in slums after they migrated their and they are treated like dirt but why ?
If you ask that drunk who accuses the dark elf of being an imperial spy and ask him why he hates them it's because they are not helping in the war which is what they were arguing about in the first place and if you play a dark elf and join the stormcloaks they have no problems with you joining and treat you the same as you are in that army as any other race , even altmer , the racism comes stems from suspicion mainly and if you talk to the dark elf merchant by the smithy in windhelm she says they gave her a hard time at first but she proved herself through hard work and they dont have a problem with her so it seems to be more of a cultural thing of proving yourself than a purely racist thing. Also some npc their , free winter i think is concerned for how they are treated but he isn't empire , we can't judge a whole nations views based on one or two people .
The kahjit on the other hand aren't allowed into the cities but those are both empire and stormcloak supporting cities and to be fair the only kahjit i seem to find in skyrim are bandits or caravaneers which if you do the theives guild questline which I learned , deal illegal narcotics such as moon sugar and skooma and will buy and sell stolen goods. People have need to be suspicious to be fair and even so its everyone that's like that , not just stormcloaks.
Ulfric
Not much to say really , he does come across that way but if you do side with him and win he doesnt declare himself high king even when prompted by galfar his righthand man , he still opts for the moot and he gets straight on to planning the defense against the aldmeri who he says will probably attack by shoreside which given skyrims mountainous terrain seems the logical choice becuase the stormcloaks know the land and with the mountains everywhere it would be easy to predict and cut off enemies and slaughter them in guerilla warfare so ulfric is no fool and misread in my opinion.
Who stands a better chance against the aldmeri
As i said before the aldmeri have a major disadvantage by land and must go by sea , either way they won't be difficult to predict and skyrims terrain and climate gives the stormcloaks a major advantage. But I should discuss why the empire is weak.
The dark brotherhood quest-line surprisingly gave me a wealth of information on the empires strength
1. obviously being the half assed , incredibly easy to kill security that was the emperors personal gaurds o.0
2. emporer knew he was going to die by the dark brotherhoods hand stating he "told them you cannot stop the brotherhood" and according to cicero's journals the skyrim sanctuary was the only one left in existence , the last one to fall was cheydinhal and that saw so little work that cicero was driven mad from boredom which led to his jester alter ego , how little faith must he have had in his own personal gaurd that he knew you were coming for him and he didn't even appoint a single bodygaurd in his office becuase he saw no point , some of the crew werent even armed

3. Cicero's journals state that cheydinhal is being torn apart by a turf war between two skooma dealers , cheydinhal ! a capital , one of the biggest cities in cyrodill being fought over by two drug dealers , bravil was also ransacked by lowlifes hence why they moved the nightmother and bandits just roam the city streets , the empire has fallen to pieces

Another few things I've noticed , you can side with hadvar who saves you at the start if you follow him yet he didn't bother debating sending you to the block seconds earlier because he didn't want to question a superior , the empire has lost it's spine , they are too afraid to stand yo to superiors like hadvar to that harlet at the beginning and the empire to the aldmeri ( during the truce negotiation they had to be present at it despite the fight being purely and empire vs stormcloak matter but only the stomrcloaks had the spine to say they had no right to be their and forced them to leave ) .
The last point leads to this one too , if the aldmeri have to be present in all empire affairs how are they going to plan an attack againt the aldmeri without them knowing before it gets too far ? I just don't think it would be possible
One last point on the empires weakness , look to it's supporters , see where their heart truly lies , wealth and power , the jarl of markarth , the battle-borns and erikur , thane of solitude , question all of them ,( Erikur at the aldmeri party in the main quest ) , they all are with the empire for money or power .
The last point overall is what the aldmeri want , read the dossiers at elenwens party , they dont want an empire victory or a stormcloak victory , they want to two forces to weaken each other to make it easier to take over , they are playing them against each other , yes they had ulfric captured and lied to him at a point to manipulate him and marked him as an asset but thats aldmeri arrogance , the same dossier states that he is uncooperative and wont speak to them , and as my earlier point above showed , he has no plans of helping them.
So that's all my stuff
I'd love to hear your opinions , especially empire supporters in case their is anything i'm missing or overlooking 

anyway yeah I think we have a distorted image of the aldmeri , they are powerful and crafty when really they are fools who don't exactly try hide the fact they aren't ready to tackle an empire that can't handle itself or take any other province by physical force , granted they are doing it in a clever way but spreading independence and pissing everyone off isn't gonna last long and again they stated they werent ready to attack despite the piss poor state of the empire who can't even stop two skooma dealers o.0