I don't know who you play with but none of them can be very good at Halo. Melee encounters were never a good idea thanks to the shiet timing system that meant there was no guarantee you would win an encounter even if you hit first and had more health. Now they've tweaked it, and going in for a melee attack will more often than not result in you dying along with your opponent in a "Double KO". Meleeing works up to about rank 5 in Lone wolves and beyond that you will get beaten badly. Going into even a lone wolves game with rank 30 people and trying to melee your way through it will end up with you getting severely raped. Going into any of the top rated players on the bungie stats pages and their number one weapon will be the Battle Rifle by a massive distance, followed by the sniper rifle most likely. Also, I am pretty sure 95% of the halo community consider people who abuse melee attacks to be nothing but nubs, and as such most people seem to specifically distance themselves from using it. As stupid as this practice is, it occurs and is a pretty large theme throughout the halo community. I really don't know where you get the idea this is a prevalant tactic in halo from.

Also, grenades have almost no effect on halo. The only maps where Grenades have any real say in the matters are Construct and Valhalla. Construct is the only map where grenades play a large part in your offense. Valhalla is only useful because 70% of halo players are too stupid to realise that jumping off a giant launcher that drops you in the same place over and over again without being able to change course means that you're easy targets for grenades. Apart from that, it's almost impossible to get killed by frag grenades because to catch someone around a corner you need ridiculous timing and good placement, because unless you get them as they are stepping around all you have to do is walk backwards and that's the end of that. Using grenades in any sort of one on one situation is only viable when they can't see you, because if they can you're asking to die. I absolutely adore people who love using grenades on halo. Throwing a grenade essentially gives you two seconds where your character can't do anything. Two BR shots on that unable to react character and you've won, every time. Stick grenades are useful weapons for combatting vehicles and if you get yourself stuck then you're either moving like an idiot, or the person who stuck you threw well and you have to take your hat off to them.