Yes. When citizens are not given the chance to vote, its legitimacy is in question even if it wins 66%, especially if it directly or indirectly causes the walkovers. If it gets 66% with an islandwide voting then a different story.
However, that is different from the argument that 66% is 33%, unless someone is very sure that the opposition would win 100% of the votes in the uncontested wards.
The assumption that with GRCs you cannot have more than one party is false. The prospect of having 9 GRCs go to PAP and 5 GRCs going to another party is not impossible.
The GRC would create a dominant party culture, but possibly a purebred 2-party culture. However, I would argue that it would create difficulty for a multi-party culture or an impure 2-coalition to emerge as it favours biggest parties around, as it is grouped results and winner takes all. For those who advocate multi-party culture, GRC would be the biggest obstacle. For those who can live with 2 parties as they think what they see in US or UK is enough, then the GRC is a lesser enemy although opposition can still be against it for other reasons.
End of the day, the entire system is only advantageous to PAP only because PAP tailored it to filter the people's voting patterns. If the people's voting patterns change, PAP's intention would backfire. Hence I would tackle flaws of the election results with the people rather than PAP. That of course does not mean PAP can't change the system again to fit with the new voting patterns, but heck, it is as if raising the "unfairness" to them has brought about any change in the first place.
if there are no walkovers, the pap will most likely have a larger percentage of votes due to a larger islandwide turnout. large turnouts favor the pap. and since oppo's (no more "the" oppo in sg because they are so frigging fragmented) don't traditionally contest in walkover wards due to smaller number of candidates and less chance of winning, their new contests there would amount to more votes gathered overall for the pap.
no matter how one looks at it from a number's perspective, oppo's in sg are screwed.