"There are were certain folk revival singers, Lloyd, .Armstrong, who used or advocated particular styles which were not based on traditional singers styles and who did not sing in their natural voice."
Are there - the two you mentioned certainly don't fit that description ?
Frankie actually ran voice workshops based on the idea that you first 'found' your natural voice, then extended it to its full potential
The human voice is much like the brain - most people use only a fraction of its capacity (I'll refrain from the joke that springs to mind :-)

Frankie used some of the exercises MacColl devised for the critics group and added more she got from listening to Eastern European singing - they were all based on traditional singing and no other styles
I never attended her workshops but I'm pretty sure they were aimed at women singers

Bert did little other than use the famous Bert Lloyd 'grin' to harden his tone, he was aware of the necessity to do so for certain songs, but had difficulty in achieving it
It was, I believe, a technique he picked up from observing Eastern European singers
There was never an example of non-tradition in his singing in my experience - that sort of thing came with the log gappy guitar breaks and the gappy breaking up of lines and hiccough phrasing or vibrao of the singers you appear to admire
As for the the unlistenable non-narrative musical mish-mash of 'Electric Soup Folk....

Bert, Frankie, and all the singers I remember enjoying drew directly from the tradition - they interpreted their songs and appeared to enjoy them as expressions of emotions rather than music with words added, as is so often the case elsewhere
Their methods of work may not have come from the tradition (any more than did your techniques of choosing your songs by speed or key) but their aim was to reproduce the songs traditionally

You say Bob Lewis has a 'folk' voice - so does Harry Cox and Sam Lerner and John Strachan and Jimmy McBeath ands Sheila Stewart and Brigid Tunney and Tom Moran and Joe Heaney.... and dozens of others I listened to (and still do)
What distinguishes them all is they are all different - miles apart in some cases - they sang like themselves
In most cases they had a way of singing that wasn't particularly varied - as you say, that is not the case with the 'performer'
When the scene was at its healthiest most revival singers weren't 'performers' and didn't want to be - we sang unpaid at clubs and we aimed to please ourselves while at the same time being aware that we had a responsibility to both the songs and the listeners to make a reasonable job of them
Our pleasure came from our having done so
This is from an intreview we did with MacColl - it sims up perfectly my feelings about public singing

“Now you might say that working and training to develop your voice to sing Nine Maidens A-milking Did Go or Lord Randall is calculated to destroy your original joy in singing, at least that’s the argument that’s put to me from time to time, or has been put to me from time to time by singers who should know better.
The better you can do a thing the more you enjoy it. Anybody who’s ever tried to sing and got up in front of an audience and made a bloody mess of it knows that you’re not enjoying it when you’re making a balls of it, but you are enjoying it when it’s working, when all the things you want to happen are happening. And that can happen without training, sure it can, but it’s hit or miss. If you’re training it can happen more, that’s the difference. It can’t happen every time, not with anybody, although your training can stand you in good stead, it’s something to fall back on, a technique, you know. It’s something that will at least make sure that you’re not absolutely diabolical         
The objective, really for the singer is to create a situation where when he starts to sing he’s no longer worried about technique; he’s done all that, and he can give the whole of his or her attention to the song itself, she can give her or he can give his whole attention to the sheer act of enjoying the song”.
(Interview tape 3).

That says it all for me
Jim Carroll