Do people eat hot food every meal? To me, non-availability of hot food during certain hours isn't such a serious problem. I guess I'm too used to lounges without even a packet of sandwiches ("crisps and nuts only" types) and that's what I tend to expect from a "business class" lounge.
Anyway, LHR T5 is not somewhere that makes people desperate for hot food - if anyone wants hot food, there are plenty of places to go, except one has to pay for it. I know what I'd do if I encounter a situation where I can't find what I want in a lounge. Heading off for a bite to eat elsewhere first.
If it was at an airport with no other facilities, I would think of this differently, but in this situation it seems fine to me.