If Singaporeans were asked in a National Referendum what the broad criteria should for an EP candidate that has custodial powers over reserves and on key appointments, I suspect that at least 90% would want someone with some level of appropriate level of experience level in a substantial role, has the gravitas, and bearing and character to act as the Head of State of the country. In essence some sort of pre-qualification or qualifying criteria but not necessarily the attributes chosen by the PAP.
The primary reason is that the country will be stuck with that person for 5 years as Head of State. Unlike an MP where there are many, a number of dud MPs elected erroneously wont harm the country much as others can carry on the show. MPs also do not have executive or custodial powers.
In India, we have movie stars as state Chief ministers and in the Philippines we have the boxer Manny Pacquio as a senator. They got elected because they are the most recognisable in their electrorate.
If its only Singapore citizen and 21 requirments, I suspect that they will be a substantial number of candidates unless the deposit amount is substantial and can be forfeited. Even a half decent candidate might drop out on the thought that votes will be thinly spread with no one getting much except the govt endorsed candidate who has the state media giving full coverage.
So the comparison between MP and EP may not be tenable.