Janus is a unit that can be used pretty effectively in some conditions/maps. Good examples are:making janus in 1v1 before mid-late / end game is a sign of noob, since the janus are so easily countered by 1 jeffy & 1 flash, and they also take your precious micro time from raiding/protecting expos/expoing, im having trouble doing just those 3 with average of 150-220 apm.
They are great for ripping samson/slasher swarms apart when nothing else gets in weapon range for long enough to do any reasonable damage before being killed by their rockets.
They are effective against flash/stumpy when the flash and stumpies are forced to attack through a narrow margin, i.e. a chokepoint or terrain where they can only go through a small area on the map, often up-hill meaning they progress slower too. (cooper hill for example)
They are good for taking out guarded defences with a more guaranteed success rate (i.e. the static defences die) than other units. Particularly against statics with higher HP such as HLTs/beamers/hllts
They are AWESOME against some T2 units, particularly those with high armour and slow speed (SUMO or CAN or ZEUS for example, and against T2 units with similar range to janus but low/med HP - such as the Maverick).
Good for picking at enemy structures/units in a situation where both players have defence lines (mainly with more structures and less units) set up close to each other.
Good at owning comms.
Good at attacking statics in raised positions (such as on small hills or pillars, e.g. Brazillian Battlefield/Metalheck) This is because they are pretty much the only T1 unit outwith nixer/wombat hovers that can do substantial damage to a RAISED structure which other units can't shoot due to range/weapon class issues. Samsons/Slashers can pick off these structures if they are small/mid range such as llt's/beamers/hllts but it tends to take considerable time due to LOS issues and low dps, by which time the enemy can bring some forces in to force samson retreat.
If you're trying to say that microing a group of janus is harder than trying to co-ordinate jeffy/flash or jeffy/stumpy groups to counter them I really don't understand your logic. Keep in mind that to counter a large group of janus you'll need quite a few assault units and quite a few scouts to pull it off effectively, which takes time to build and co-ordinate an assault, and the micro required to counter IMO vastly outweighs the micro required to use the janus in any of the above situations that favours them, which is generally where you see them used anyway.
Sure, its pretty stupid to build janus early game in 99.9% of 1v1 games, but I certainly wouldn't go so far as to say that mid-game janus is noobish. Note that I am not a player that tends to use janus out with very occasional circumstances so I'm not trying to defend them because I'm a fanboy, although I have observed them to be very effective more often than not in the above situations.
Oh and, SPAM CLICKS FTL SLEK.