The Cybex Pallas (and the Anoris which is the one with the airbag) is subject to a rollover test just as all other car seats sold in the UK are. It is a static inversion I believe rather than the seat needing to be placed into an actual vehicle and rolled - that would be too expensive as it writes off the vehicle. I know that there is a video somewhere on the internet showing a crash test dummy coming out of a seat like this in an actual vehicle rollover test (which as said, is prohibitively expensive, so rarely performed). OTOH 5 point harness seats are excellent in rollovers - basically 0 problems, provided they are used properly.
The newer standard (R129) is slightly stricter on some aspects of the impact shield seats - some of the R44 ones often had issues actually engaging the pelvis of younger/smaller children. The newer standard addresses this and should hopefully offer better protection in rollover crashes, and possibly offset crashes (where you crash head on but only part of each car interacts, common in e.g. overtaking accidents or when someone is too far into the opposite direction lane).
The data from real world crashes shows that impact shields, even the older ones, have roughly the same overall performance as 5 point harness seats used forward facing. So the claims that the companies used to make that they are "nearly as good" as rear facing are not really correct. They do have lower neck loads than a forward facing seat but this is offset by the fact they have higher ejection rates which tend to be in those rollover/offset crashes, and higher abdominal loading. However the other thing in their favour is that they are very rarely misused. The data on this is back from when all the seats were R44 and they were all fixed with the seatbelt itself directly holding the shield in place. These days with the R129 ones the shield clips into the seat using belts integrated into the shield and must be tightened. I don't know if those are harder to use. I used to have one of the seatbelt ones for DS1 (now 17!) - He was quite happy with the shield, but I think he too would have protested being taken in and out multiple times in a row.
My gut feeling OP is that your DD is reacting to being restrained and she is being a very typical toddler. You have taken her out of the seat for a short time and she understandably doesn't want to go back in. I would probably use something like bribery (e.g. let her choose a favourite song, let her hold a special toy, reserved only for the car, or have a snack) and try to increase time in between car trips so she has a chance to have a play/run around/be in control etc before she has to go back into the car. I appreciate it might not always be practical to do that. But it's quite likely that there is nothing wrong with the seat itself, except that it is boring to be stuck in there.
It is also possible she could be experiencing the beginnings of car sickness - some children start to have this around the age of 2. It could be worth getting her eyes checked as car sickness can be associated with short sightedness.
If you're driving on country lanes then offset crashes are more likely, rollovers are also I believe more likely in a 4x4 type car, and so on balance, a very good 5 point harness seat is likely to be better than an impact shield. Maxi Cosi is a good brand and their seats perform well forward facing. The support leg of the Mica does the same job as a top tether in terms of reducing forward rotation. Straps should be level or slightly above shoulders for forward facing. Don't put her in the seat in a coat - it's uncomfortably hot and it will make the straps too loose, even if they seem pulled tight. Unfortunately it could be the combo of being taken in and out of a coat and the car all at the same time - if you have a thin coat like a fleece for this reason, maybe open windows to keep the car cooler, remember car seats are often lined with a polystyrene type material which can be hot. At 2, forward facing is not so risky that it must be avoided. Yes, rear facing is better to the point it's worth some mild inconvenience, but it's not worth battling against extreme distress. (You probably know most of this already, but just in case!)