Ex Check Pilot here.
Furthermore, are inexperienced pilots such as myself, expected to nail the first attempts in OEI given that we have not done any OEI flying at all for the whole 6 months?
Nail it, no. Proficient enough to demonstrate that you won't kill people should it happen in the real world, yes. Most instructors and check pilots are not looking for perfection. They're looking for not below average.
with no time to adjust to the different feel of the simulator, being a CEO variant whereas I fly the NEOs
Regardless of aircraft variant or type, I found only newer pilots within their first year or so complained about the difference between an aircraft and the simulator. You will eventually learn how to "fly" the simulator, and you'll simply adapt to that. I know a few guys on these forums will say a simulator is no different to the airplane, and for about 90% of the material, they're right. But I've always found I fly a sim slightly different than I do the airplane, regardless of what I fly on the line and what the simulator is modeled after.
Furthermore, no time was given to adjust to the difference in the feel/ergonomics of the control
No one will build in time except maybe Day 1 Initial for you to get a "feel" for it; simulator time is too valuable. This is something that in the beginning you just have to live with. Again, eventually, it won't be an issue. I will grant you though, that some of those older simulators can be a little clunky.
I want to know if its normal for new pilots to struggle in their first few OPC/LPCs? or is it uncommon for people to struggle?
Struggle is an interesting word to use here. Is it common for people to struggle? No, it's not. It happens, but it is not common.
Is it common for newer pilots to demonstrate "loose" flying skills? Yes. And what do I mean by "loose flying skills?" Enzino references centreline control above. Most new pilots show some difficulty with centreline control as they finesse the ability to "squeeze in rudder pressure and hold" (a technique I 100% agree with). It takes a while to identify what that pressure is for the various conditions of each aircraft type. However, you will eventually reach a point where you lose an engine and you don't let the nosewheel drift away from the centreline. In the meantime, while you shouldn't chase the centreline, focus on rapid identification and prompt rudder input so that you minimize the drift. With that said, paralleling the centreline does not give you an open field to do with as you please. I've been witness to many unsuccessful flight test attempts because in paralleling the centreline, the pilot allowed the main gear to drift off the side of the runway or, because of poor rotation technique, they let the airplane settle back on the ground and because they were off centreline, this settling occurred off the runway rather than on the runway. Parallel the centreline to a point. If one of your main wheels is sitting on the centreline, that's a drift that is too far, and it's time to ease the nose back. But, this will come with time.
I used to tell my students back when I was still instructing that everyone will have good days in the simulator, and everyone will have bad days. I've had to deliver the bad news that a pilots performance was below standard to inexperienced pilots and extremely experienced pilots alike. The best thing you can do at this point is to study your procedures and hand-fly the airplane during routine operations as much as your Captains and company are comfortable allowing you to (within reason of course). That familiarity with how the airplane handles during two-engine work will help you progress during your OEI flying in the simulator. If your company allows you to, you could also look to pick up any overtime in the simulator rather than line flying. That will give you more exposure and more time to practice. Just remember though that in these cases, you're only meat-in-the-seat and the focus would be on the other pilot, and you still have to bring your A-game to help the other pilot. If your company does not allow this, that's too bad - so instead, talk to your Captains and see what suggestions they have!