2. the nature of the problem statement "needle in a haystack" suggests obstacles to traditional text search, eg. too many false positives to be helpful for natural searches and challenges to constructing more specific ones.
language models introduce new possible solutions to this ie semantic search. poorly-designed chatbots could be worse than a basic search, sure
2. Yes, but its difficult to get a chat bot to function well over the wide range of services a government offers and the wide range of users who need government services.
One of the most annoying chatbots I have ever come across was on a UK government site. The DVLA. "lets tell you what you already know and not answer the question".
Possibly something well designed might make it easier, but I have found most of gov.uk to be very usable and helpful.