"I really do think Life rafts are pish compared"
Yes, but you are not considering the likely circumstances.
The facts:
Most pilots will not wear suitable clothing underneath a dry suit. Why? It is uncomfortable and they are not aware of the importance of doing so.
Most pilots will leave their dry suit unzipped. Why? It is comfortable. They are not aware that they may struggle or forget to do it up in a ditching and they are not aware how serious the consequence of not doing it up are.
Most pilots, even if they have a dry suit for their personal use, are unlikely to have suits for their passengers given the range of sizes potentially needed and the cost.
So, whilst I do not dispute dry suits used properly may provide as good a survival tool, realistically few pilots are likely to buy enough for them and their passengers or use them properly.
Life rafts
Most pilots are aware that life rafts can be bought or hired.
More pilots are aware that they are no longer bulky and are large enough for them and all their passengers.
Few life rafts are sold without a canopy.
Life rafts are therefore a convenient alternative but do they increase your chances of survival?
The facts:
Hypothermia we agree is the biggest risk. Air temperature, being wet and most importantly wind chill contribute to hypothermia. Once in a canopied life raft, radiant heat from the occupants, protection from wind chill from the canopy, the ability to remove water with sponges provided, and with any luck an air temperature that is warmer than the sea combined with the benefit of some solar radiation all contribute to reducing the onset of hypothermia compared to being in the water (with or without a dry suit). Hopefully you will also find there are foil blankets provided.
Moreover, you now have a platform to keep the group together, to support those that cant swim or who are poor swimmers and from which to operate any other rescue equipment you may have (epirbs, flares etc).
Compare that scenario with a pilot in the water who forgot to do up his dry suit, and is wearing a t-shirt and jeans underneath, cant swim very well and is scared of being in the water, a couple of passengers with him who are only wearing life jackets (the pilot didn’t have any extra dry suits), trying to stay together and operate the flares and epirb they some how managed to hang on to which are now underneath the water in a rather cold hand!
In short there is no perfect solution. There is no guarantee you will get out of the aircraft with the liferaft, or get in it when you have got out. However I submit a raft provides most pilots with the best and practically most realistic way of improving their survival chances in a ditching (short of course of the yellow brick afore referred).