I'm a casual player, mostly grinding tanks, not playing a whole lot of T10 or ranked. Those x5 missions are a great way for me to push down a line but are implemented in such a way that it also prevents me from doing what i want.
Fancy doing a second game on your favourite tank ? x5 mission down the drain for no reason.
Fancy giving a campaign mission a go ? x5 mission down the drain for no reason.
What i wish for is that those x5 missions would be implemented as extra Manageable Bonus to Experience. That way it still only works for wins but you get to choose when to use them instead of spending them on a win you don't care about.
I know it probably doesn't mean much to a lot of people but i'm curious to know if more people don't enjoy wasting those x5 on tanks that don't "need" it.