No idea what there is to agree or disagree with. Uk is not part of the eu, never mind schengen.

the uk government decides what it considers clean.

If you transit in the uk will need to clear security

If you do not like it there are other airports in europe you can transit through. my experience, MUC is about the best.

i agree not clearing security is preferable to clearing security so i am always pleased when my uk or us flights into fra arrive into Z rather than b or c.

in terms of the the original posters question, the rules have not changed significantly since the last time they transited the uk. If they follow the rules then security, and the rest of the transit experience if it is within one terminal, is relatively straight forward at lhr.