Peterh - just to chip in on that new line of debate I also dont disagree with you, because there are almost always exceptions to a general rule.
The younger you are the faster your reactions so arguably young low hour pilots might adapt to high speed aircraft more quickly.
I think "techy" people pick up glass really quickly, those not, well struggle for a long time.
Those are just two examples of why there are exceptions to any general rule. However if you talk to those who routinely convert pilots to a Cirrus they will tell that low time pilots with a background of the typical training GA aircraft take more time to adapt to high performance SEPs.
Moreover I do think the cirrus is a little different to many high performance SEPs. It is more slippery and without the luxury to dump the u/c, flaps or speed brakes so pilots are even more likely to be hot and high, the side stick is different (nothing more) compared to the conventional yoke with which most low hours pilots will be familiar, many high performance SEPs still have conventional six packs so however you cut it there is one less thing going on there as well, and the landing profile is a little different.
You may well have found transitioning to a Cirrus more difficult than a TB20 those years ago, perhaps not a whole lot, but never the less more of a challenge.
Moreover its one thing flying the thing another being comfortable. I reckon flying a DA42 is a very easy way into twins and anyone who has flown a DA40 will find it easy once they have adjusted to the extra speed and the size. A Seneca or Aztec is in theory no different but I reckon most pilots will find either a real handful to start with, if for no other reason than "the systems" come from a different age, are not necessarily intuitive but when things go wrong you had better be familiar with them.