I think you will find that opinion on this will differ depending upon what type of MP game the person wants to play.
For those who play a LOT of MP (HoG being a prime example), and have done so for a long time, I can understand the frustration of repetitively replaying the same tired old strategies. If you are Austria, you are totally Land, if you are England you are totally Naval, and England (straits or no) will never be on the Continent without massive help from an ally, and Austria will never be colonizer overseas (unless protected by an ally).
I disagree with HoG that this means the game becomes ahistorical; indeed, look at who DID colonize: Spain (until the Armada was destroyed, after which they were just hanging on to their original claims of mostly not such great land), England, France, Portugal and the Netherlands. And to say that France colonized is a bit of a misnomer: France claimed lands in which they engaged in trading, but they never were true colonizers like England or Spain, until after our period is over and the focus shifted to Africa. This is one of the primary reasons they lost their North American possessions in the series of 18th Century wars fought in Europe with colonial side-fights.
But, what it DOES do is take the choice away from the situation. You can't create a different colonizer with a different country through your Domestic Policy settings, without being at a serious handicap in the process. Thus, while there were good reasons that the Swedes failed in their colonization efforts, it wasn't through a choice to support land forces over naval forces. Yet, in the game, this is precisely where the trouble can lie. And THAT is quite ahistorical: it wasn't pre-ordained that the French wouldn't be as powerful colonially as England and Spain, nor was it strategically the only reasonable result.
But there will be a camp of people who will not see this as a problem. Why? Two possible reasons: One, they don't engage in much war. When you boil the Land/Naval slider debate down, it comes down to the effect upon Land Troop morale, and the effect THAT has upon the ability to compete in a game involving lots and lots of warfare (which, I might point out, is a historically accurate game

). No warfare, no worries about morale. Two, they haven't yet tired of the "normal" situation, enjoying still the spread of red and yellow (and maybe green) across the globe while White and Blood Red and Blue fight across the European landscape. For them, the creation of this situation, a dull repetition for the "old hand," won't cause any concern.
My opinion is this: I don't like locking the slider for the simple reason that I don't think the morale issue should cause people to throw the baby out with the bathwater. Yes, the slider is loaded with wayyyyyy too much effect, but some of that should be available to the player. Perhaps the slider shouldn't be locked, but allowed some room (say 3-7). But if the trouble with your games is that England is always full Naval, and you see this as an issue, then what you really need to do is change the diplomatic situation.
