I will try to be more clear:
About the strategy:
Yeah you should goes for the first two lines, try to finish at least one of them in 5 rounds. Alternatively, you could lose your 2 points extra for the line and be in a position where you think you will score more than the opponent(s) in 6 rounds. If that's the case, you don't have to finish a line in 5 rounds. But that mean that nearly everyone else should be in a position where they would lose in 6 rounds, so they should try to finish a line in 5 rounds. And that's what you should be doing if you want to win.
About the design of the game:
I feel like if per example you decide that the game is played in 6 rounds, then at every round you are still incentive to play in your first two lines to be able in rounds 4&5 to still have the choice between playing on those lines on that round or not (else if you skip your first line round 2, then in rounds 3/4/5/6 you are forced to play in that line or to lose 2+ points).
Furthermore, going for all in one color give you much more time to try to get the +10 bonus, I don't have enough experience to know if that would be better or not, but my instinct said that it's too rare with 5 rounds to be able to put pressure on that bonus at high elo.
(+ what I said in my previous post about how weird is it to put a rule (unknown number of rounds) with in my opinion no effect (5rounds every game))
edit: not to mention that with 6 rounds, you could have some rare spots where you want in purpose to not finish/not do a line to score more points with it later on.
About the strategy:
Yeah you should goes for the first two lines, try to finish at least one of them in 5 rounds. Alternatively, you could lose your 2 points extra for the line and be in a position where you think you will score more than the opponent(s) in 6 rounds. If that's the case, you don't have to finish a line in 5 rounds. But that mean that nearly everyone else should be in a position where they would lose in 6 rounds, so they should try to finish a line in 5 rounds. And that's what you should be doing if you want to win.
About the design of the game:
I feel like if per example you decide that the game is played in 6 rounds, then at every round you are still incentive to play in your first two lines to be able in rounds 4&5 to still have the choice between playing on those lines on that round or not (else if you skip your first line round 2, then in rounds 3/4/5/6 you are forced to play in that line or to lose 2+ points).
Furthermore, going for all in one color give you much more time to try to get the +10 bonus, I don't have enough experience to know if that would be better or not, but my instinct said that it's too rare with 5 rounds to be able to put pressure on that bonus at high elo.
(+ what I said in my previous post about how weird is it to put a rule (unknown number of rounds) with in my opinion no effect (5rounds every game))
edit: not to mention that with 6 rounds, you could have some rare spots where you want in purpose to not finish/not do a line to score more points with it later on.