I would say that one con of this system is that you are using a vote for a specific candidate as an indicator of support for the party as a whole. (politics.stackexchange.com)
The answer is that their prominence has not made them immune from the decline in support for their party. (lordashcroftpolls.com)
It pointed out that younger people are much less likely to claim support for a party than older age groups. (politics.co.uk)