If there was a traditional system without exploding offers, a school like City may well need to offer twice as many places as places exist. Many schools will need to do this in urban areas. It might seem like massive over offering, but once you consider that many have applied to 4 or 5 schools and can only accept one, you see how many declines each school will get.
So if City offered to say 200, it could be that 100 at best would accept.
Regarding the WL, no doubt there will be many on it for whom City was never their top choice and still isn't - but people like to think that they are keeping their options open. If and when City goes to WL, they may well find that they make offers and people decline - because they never had it as top choice, or they did but have accepted another offer they received. All of this is totally common with traditional waiting lists. What City has done is to try and reduce the no of places they need to fill from WL, hoping that the vast majority of the 75 acceptances are genuine. It's not so bad to have to fill 10 or 15 places from WL, from a pool of candidates who met their required standard. With the traditional system, they may have decided they could only over offer slightly to avoid the bulge class - perhaps 100 places, but then there is a possibility that the majority of these have one of their other 4 or 5 choices top, and acceptances are only 30 - so then there's a big need to use the WL and to go far far down it. This is what they have avoided.
Re WL and not being especially high on it, I would say that they won't need to fill huge numbers of places from it this year - some will have paid £1500 deposit and not take up the place, but they will be fairly small in number. A few places will become available, but they may have to go quite far down the list to fill them in actuality as many have take others, so not being at the absolute top might not matter. How have they ranked the list ? Is it by speed to get on the list or score in exam?
One final thing, it may well take longer to get to WL this year - those who paid £1500 to secure a place who later give it up, may take longer to do so - right up until Easter, when they would owe a full term of fees. Why? Because, having paid, they feel no obligation to be speedy in releasing it and may well sit on the City place, as well as another independent they have accepted and intend to take, or a state Grammar place. Having accepted and paid, and especially if they felt pressured to do so, they may delay releasing the place until the very last minute, meaning only then can City go to WL if they decide to do this.
Quite a few schools don't use WLs. They know that over the next term or so, people move into the area and contact the school about admissions and that they can test them, find people of a good standard and give them the places - these schools though tend to be more flexible about space and numbers and so can take an extra few late comers if they are great candidates, or not bother and just have a smaller year group if they're not so good.
In the end, what does this mean for people waiting? There will probably be a longer wait than previously. The consequences of not getting those forms in are perhaps more significant than people first thought, if they are still holding out for City. Not what people want to hear, who still really want City despite everything, I know, but likely. Other schools will go to WL on 5 March if they need to. City might not get their declines until Easter.