I'd say confidence and recognition you are in a niche area and as such people come to you in an hour of need, you are the expert / safe hands. Not every day this is needed. As if this was the case every tom, dick and harry could be doing your job. Given this opening statement it is normal to have a gap.
"How do you deal with a gap in your CV? For some instances, like when I had recent contracts, people knew me, so there was no need to explain anything. But for 'normal' applications, how do you deal with gap in CV?"
So assuming you have a Ltd company being a contractor ? What I'd do is:
Jo Bloggs Ltd March 12 - Present Day - Director (looks continuous and is)
Various roles for clients such as.......
Senior Womaniser British Gov responsible for....
Chief Comedian French Interior Long Leg Ministry responsible for
National WAN designer Yorkshire etc etc no need to put dates
Obviously pick your best projects / roles relevant to what's happening in your industry today - such as AI/Cyber Security Chief LAN/WAN designer if there is such a thing
Then I do recent clients:
Big Four name, Cabinet Office, Scottish Gov, BT etc
No need to get hung up on not working for 6 months last year - your LTD company continued to pay you, you've been so successful that you can afford to do some training and went on holiday after 4 years full time or whatever
You do list short contracts in CV? - See above only if it was a blue chip / current that adds to your cv. WAN/LAN architect Slough Council vs WAN Cyber Security Architect MI6 UK Gov
How do you convince employers that you are happy to accept a role a few rungs down the ladder?
That's why you list the various roles as stated above. These should range from Top Dog down to minion. Then you can point them to your cv as evidence you have done it before. Then have the soundbites ready for how good it is to meet and keep skills up to date by being more hands on. In fact it was by doing this and working with a new graduate I realised I had a gap in my knowledge and did some training on X.
Hope that helps