1.) LAND MOUNTS need higher JUMPS/ climb option:
A large number of players doesn't even use land familiars since flying familiars cover the transport need much better. Outside of Fractura hammer-throwing boss, avoiding hammers and Stygea travelling land familiars are losing their purpose. I remember when I was in ellora sanctuary fighting those tree-enemies from a back of a land familiar and there were trunks laying on the ground in the area. the mount couldn't jump over the trunk making me unable to draw back and gain distance between the enemy. After I killed it i went to the trunk and barely managed to somehow get the mount over it.
i don't mind boulders and things like trunks, obstacles on map, they make it seem beautiful and alive but compared to the jump a regular character like wizard can do, height of jump and distance compared to character size, while on the other hand looking the jump of land familiars compared to their height size, it seems like character herself can jump better than her familiars. It is more like land familiars are hopping instead of really jumping in the distance.
it would make land familiars much more fun to use, if their jumps were actually usable to jump over something on map, especially talking about heroic and legendary familiars. they should be able to jump over a trunk, river, or make a high jump that would put them on top of a house in town. If you want to get on a rock on the map with your land familiar, that rock basically needs to be smaller than the familiar or you cant get it up, not without using a flying mount and that is pretty sad.
I believe giving land familiars longer and higher jumps would bring players much more fun with using them, to travel with them and explore the map designs.
2.) FLYING ACROBATICS
When getting off the flying mount (wishing to land) all players just jump off their mount and let the gravity hit them to the place they want to land. Gliding on flying familiars is possible only in one direction: forward and that is a big limitation. basically you need to go slowly up to the height you need, then dash forward for speed. It would be much more fun if glide was possible in diagonal directions, not only forward. Allowing flying familiars to swoop down towards the ground, and rise some dust around them also. The flying system is really limited with gliding being able to be sued only in forward direction.
Compared to the game School of dragons for example, there your dragon can fly in any direction, giving a player much more freedom in the air (although possible speed there is bad). A dragon can make diagonal glides without losing speed when changing directions. In Icarus flying somewhere always means gliding forward. I want to see the glide speed while the mount is descending, swooping towards the earth and moving in diagonal directions also.
3.) GENERAL ROLE OF THE FAMILIARS/ PET SYSTEM
when I first watched Icarus trailer and started the game, I didn't expect all the familiars you can get will mainly be a mean of transport. I have been over six months in the game and the game is starting to feel like >gotta catch them all< but the questions WHY is standing out. the familiars we tame are like stickers in beastiary for collection rewards, a stat bonus as pets or a hear-slot (seal) bonus for character's stats. So outside of transport the other main role familiars do is stat boost.
Looking at the mounted combat, aside from stat boost, the familiar is actually just standing around. It doesn't doesn't do anything itself to help in the battle. When you sue a familiar in pet status, its main role is again stat boost plus if you set it on attack mood and it stays alive in boss-battle for two minutes I guess you can consider yourself lucky. Watching the Icarus trailer i actually expected the familiars to have a more active/companion role in battles, not to just stand next to you and give you a stat boost.
Looking at the pets enemies use in game like those leopard masters around Fractura, and elite enemies in front of it leading dennivans and bajarn with them. those enemy pets actually have their size walking by their masters, while character's pets get minimized. Enemy's pets also act like individual enemies, doing normal damage, while if your pet kills a minion in low-level dungeon, it is most it can do. the damage it does to bosses is practically invisible always, and then it dies within 2 minutes and you lose the stat boost.
I would like to see the familiars actually being helpful in battle with doing damage and distracting bosses instead of standing around for stat boost. Maybe dividing pets into stat-boost pets and battle pets that could actually do damage comparable to character and have a value in boss battles. making their size comparable to character as well.
I understand this is a MMO and players are meant to team up together but lets be realistic. For some time you will have a group joining you. after some time, certain members of group will stop being active. At the end, nobody of them might be active. players with high dps dont want to do lower level dungeons. And if you manage to convince them to help you, they will do it like twice or once a week, you will be alone the majority of time at the end no matter how you look at it. If battle pets could count as another-character by taking a space in the party I wouldn't mind that. or putting a rule if you use a battle pet that the dungeon can be entered only solo with it. I mean anything would go with me, but a game that concentrates on taming familiars should give those familiars a more active role in battle system. This way they are just like pretty stickers in beastiary or taking space on parking on victory plaza, showing off what you tamed and the thing you tamed is nothing but a stat boost.
not a big things to complain about, but can make life easier a lot 
full green but isn't tame, then keeps going and makes you fail it even with a full green bar. great game design there. 