Path of Exile is always online and suffers problems.
PoE gear is more RNG based and getting upgrades is harder and takes longer.
PoE has no physics and fighting feels less fun.
PoE lore is less interesting (at least to me). GD feels like a mix of D1 and D2.
PoE has more passive and active skill available and you can do more crazy stuff.
PoE has dedicated servers and you cannot cheat easily.
PoE is bigger and has an endgame (maps) but it is RNG based if you can access that endgame.
1. Path of Exile is always online and suffers problems. -
True. It was significantly improved with the 2.0 release where lockstep mode was introduced. Now if you have low ping (Up to maybe 80ms?), there is no significant lag or any problems of the nature. But you will still get the occasional server problems, such as maybe some connection problems, a ping spike or a rare disconnect. Those are rare, and you can always reconnect to a different, hopefully more stable server in an instant.
2. PoE gear is more RNG based and getting upgrades is harder and takes longer.
Only if you discount trading which in Grim Dawn is nearly non existant and quite pointless in the sense that any person can very easily "cheat" any item into the game so items have no value whatsoever. Thats the consequence of Grim Dawn being offline game for the most part.
Also, gearing in Grim Dawn is all about Empowered relicts and Legendary items. There is a very little use for rare items as Empowered Relicts and Legendary items are in the vast majority of cases more powerfull than rare items (Except maybe some weapons).
3. PoE has no physics and fighting feels less fun.
True. And it is a significant advantage of Grim Dawn. The melee feels better, its more visually pleasing and interesting. In PoE, the combat is a bit dull, slightly above D2 in terms of non existance of physics etc.
4. PoE lore is less interesting (at least to me). GD feels like a mix of D1 and D2.
Very subjective thing. For me, Grim Dawn's lore is boring. And the set of monster you fight is less diverse and more in vein of the standard cliches like Orcs, General Undead, Demons, Bandits, Cultists.
5. PoE has more passive and active skill available and you can do more crazy stuff.
True. And it will get another layer of this with the expansion on 04.03. In my opinion, Grim Dawn's masteries are too limiting, in both the fact that you can take only two at the same time (Balance reasons, I understand, but it limits the number of builds without a doubt) and the fact that you have to invest skill points into the generic mastery bar that gives you base stats to unlock your skills. People often criticize PoE skilltree by saying that its full of meaningless +10 strenght nodes, but Grim Dawn does the same thing by forcing you to spend a certain number of skill points to get to the skills you want.
6. PoE has dedicated servers and you cannot cheat easily.
That is a big advantage of PoE for me. In Grim Dawn the cheating is unbelivabely easy and it kills any notion of competetive play because you will never be sure if the guy is better than you or just cheated himself the best items in like a minute of work. Grim Dawn is ok if you want to play solo and just finish the campaign a few times, but comparing high level characters tells you nothing about the skill level of the player, or the amount of work he had to put to create that character. Its a big turnoff for me.
7.PoE is bigger and has an endgame (maps) but it is RNG based if you can access that endgame.
Its true that maps are RNG based, but only the top tiers are difficult to acquire. Anything up to tier 10 (of possible 15) is relatively easy to get and maintain. And maps of tier 5 and lower drop like crazy, to the point that you will have stash tabs full of them if you need them.
Compared to Grim Dawn's endgame, which is Running steps of Torment or the new Void dungeon, PoE endgame is easier to get access to. In Grim Dawn, you need to craft a skeletal key to open the doors to those endgame dungeons, and the materials drop less frequently than maps in PoE (Except the top tier ones). Also, the end game dungeons in Grim Dawn are always the same. The only difference is that the ways through them are different, one passage might be open this time, and closed the other time. There is a little variation and the monsters you encounter are always the same type etc. You have no incluence upon any of this, as opposed to PoE where you can influence both the type, number, strenght and special propertiers of the enemies, and the maps themselves.
All in all, I prefere PoE for its complexity and amount of crazy things you can do with it. The longevity, the endgame, the different gear choices (Rare items are good here) and general look. But Grim Dawn certainly is not a bad game, I played a couple of hundreds of hours of it, and enjoyed it, so you might enjoy it too, possibly more than PoE.