Yes Summoners have the easiest time in both PVE and PVP. You can do Mushin to 6th flr with a Summoner with mediocre gear without knowing how to do chain CC with the class or even how to do a proper DPS cycle with it, just by relying on the Cat’s taunt and kiting. You can go around beating people in low bracket Arena without fully knowing the class mechanics and just spamming everything.
But when it comes to playing the class to the maximum potential. Summoner takes quite a while to get used to. But when I played my old BM and Sin main back in TW. In PVE, things get simple when you’re used to your BNS Gold. Because you only have one job to do, as a Sin my job is to deal DPS, nothing else matters, all I needed to do was see hostiles, deal as much damage to hostiles, avoid things that could kill me, that’s it. BM was slightly more complicated, see hostiles, make hostiles stick to me, and don’t die. When you know what to do and how to play the classes, those were the only things you needed to do. All classes are easy once you’re used to their kit, you’ll have muscle memory to handle the combos and which buttons to press.
On a Summoner, things are a bit different. Even when you’re at that point where you’re used to the mechanics and knows what and which skills, combos to use, you still need to be aware of everything; you need to know where your cat is and what’s he doing, unlike other classes you can’t just instantly CC stuff whenever it’s needed, you need to watch the cat and wait til he gets there, you need to know where and how your party members are faring throughout the fight/dungeon, whenever someone died, it’s your job to res them without completely screwing up and pull dangerous things to his BNS Items, whenever someone’s about to die, it’s your job to keep him alive; without actually dying yourself; and still, with all of these, you’re still expected to deal DPS as much as possible.
Summoner is not easy to master, but it has the easiest time while you’re learning to master it. But as with everything else, all comes with experience. I’m betting everyone in this forum who have played their main for a while would know what to do regardless of what situations they’re facing.