The plan you mentioned would work for a brand new recruiter, but in all honesty, I've never seen as low as 30%. At the agency where I worked for many years, the newest recruiters started at 35%, then went to 40 and then to 45%. In their second year, they had chance for 50%. Recruiters with more than 5 years experience always started at 50%, so I can understand your senior recruiter not considering anything less. Seniority makes a big difference as you don't have to spend the time with those people as you would with a more junior person. Plus the reality is with the internet and other contacts, it's not difficult for a senior recruiter to go on their own and make 100%. For that reason, I've seen senior recruiters start at 50% and go as high as 70-80% depending on their volume and seniority.
How much will the draw be?
I think 50 to 60 % if you want someone real good. If they are good they will pay for them selves.
You could also try $2,000 per placement. Flat fee.