using lootas makes me sad because they aren't aggressive enough for my usual orky tastes.
That said they can be amazing in team games, and are often crucial in 1v1 warboss play as well.
Most of the ork T1 is very high damage and deal with infantry armies very well, but has trouble scaling to deal withy fast vehicles. lootas completely solve this problem, while letting you hold down large chunks of the map in T1 without having to bleed from shootas or sluggas to keep the real estate.
Lootas can be awesome in team games with a bunch of waaugh banners behind them. the stealth makes them tough to dislodge from cover, and sluggas are great at chopping up any jump troops who try to counter initiate.
Cyris had a lot of good points, another is this: sometimes in 1v1 you dont want to get stormboys (vs warp spider exarch or plague champion for example) and lootas give you a lot more freedom in build orders since you can hold the map after pushes instead of having to constantly be forcing the enemy out of defended positions.
Their range is standard for suppression teams, so im not sure what you're complaining about there. some food for thought:
lootas do more damage than any other suppression team in one burst (390 where 300 is standard), but less dps overall (208 where 220-240 is standard). so they're much more of a bursty setup team than most. added to this is their range modifiers. they have lower range modifiers at long and distant ranges (.2 instead of .3), but are much more deadly up close (1.4 and 3.5 for medium and short range isntead of 1.25 and 2.75). so really, lootas are best at dealing a lot of damage in a short time over short ranges. fortunately, they can infiltrate! what this means is that you can set them up just behind any point you hold and infiltrate and wait for the enemy to come decap. a lot of times you can deal half or 2/3 health damage to a squad in one burst, if they aren't paying attention you'll wipe them in no time.
if you're losing models a lot, try to play more defensively with them: stick them in green cover and infiltrate, then push up with shootas. once the enemy starts to engage, pull back to the loota cover and you'll have a huge edge in the engagement. really cannot emphasize how good their infiltration is, it lets you use them a lot like havocs under worship, and i'm sure most people know how powerful that is (except hastaga it would seem

).
their beamy deff gun is just about the hardest AV you can get, since it deals 240 armor piercing damage per shot. that's a razorback dead in 2 shots (1 with rear armor) and walkers will take huge chunks of damage. this is one of the areas where orks usually struggle, since tankbustas are fragile and slow, but with infiltration the beamy lootas can ambush vehicles really well. if you set up and infiltrate as a vehicle starts to push up, you can let them move up halfway through your firing arc and then go to town.
try using double sluggas into lootas, push up and win map with the sluggas then hold it with lootas in cover through T1. if the enemy pushes your sluggas can charge into the suppressed units, or counter any attempt to force off the lootas.
I've been playing a lot with them recently and i've been quite impressed.