Scaling your business usually requires that you bring in more people and inevitably more experienced people in leadership roles. Those hires will need to be motivated through a combination of opportunity (equity, bonus, career advancement), compensation (base salary, benefits, perks) and environment (responsibility, prestige, office culture). You will end up giving some equity to them for that reasons (and only that reason - the fact that they were there on "founding day" is truly irrelevant). How much you give depends on the person, role and state of your company. If the role is important enough and your current status early enough then they might very well end up with half of the equity. Or more. Or less.
So go and hire the right person. The rest will shake itself out when you negotiate compensation...