Honestly, I'm not even sure why I'm bothering to type this, seeing how this thread has devolved into a personal attacks, but I'll throw my two cents in anyway.
First of all, I don't think that the first two and a half minutes of Turf War are completely meaningless. If your team controls 70% of the map going into the last 30 seconds, you do have an advantage. The point of contention lies in how much of an advantage you're allowed to hold.
In a race, if you've already lapped the other racers and you continue to drive faster than they do, you continue to get further and further ahead. In a basketball game, if your team is already leading by 100 points halfway through and you continue to outplay the opposing team, you gain even more points on the opposing team. There's no limit to how far ahead you can get. That, however, is not the case in Splatoon's Turf Wars. If your team wins the opening skirmish in the center, wipes out the other team, and gets a spawn camp going just 1 minute in, you're already as far ahead as you can get. Regardless of how much you outplay the other team at this point, the most you can do is to merely maintain the advantage you already have. And due to the nature of the game, which allows quick swings one way or the other, that maximum advantage that you can gain is not enough to assure victory.
The other major issue here is the quantity of gameplay that goes into determining the result. As a said before, I don't think the first two and a half minutes of Turf War are meaningless, but I do think that they are worth less than the last 30 seconds. This has the effect of making it so that the losing team always has a chance to make a comeback, regardless of how badly they played earlier. And while this structure of making everything come down to the final play makes for good TV, it goes against the competitive goal of determining the best player overall. Competitive tournaments never determine everything with one short match because it is entirely possible for less skilled players to win out short term. It is far less likely that less skilled players will prevail in the long run, which is why longer matches and sets of matches are preferred. In theory, you could achieve a similar effect in Turf Wars by playing many matches of Turf Wars instead of just a few...but wouldn't it be easier to just use one of the other modes, which rewards good play more evenly throughout the entire match?