I'm not going to quote anything specific, as each person's argument against chumby is of a similar vein...
But Chumby is correct.
Necrons rate as one of the lowest of the low lists as of now.
Daemonhunters suvive by dint of allies...thus making their list, if purely DH, a chosen weakness.
Same applies to WH, and they are even viable as pure sisters (or nearly pure) though shortlegged. Include allies, and boom ....they're more than just fine.
Necrons have no buffer for their innate weaknesses.
You can say any one unit in the 'dex is AWESOME...and then you have to confront one sad little fact...their only troop is the warrior.
18 point warrior
with an init of 2.
Welcome to assault, you are wiped out...
welcome to second assault, you are phased out...any questions.
You CAN ignore pariah...they cannot 'port or WBB...and they're more expensive than Immortals.
You CAN ignore C'tan...they cannot 'port, and consume a significant enough portion of the 'cron army that you merely need to focus on other elements to get the job done.
You CAN ignore any of the units you would want to (the non-necron models) as if you are playing proper 5e, you are mobile...or capable of putting forward mobile tarpits...
You CANNOT take any one unit in the codex, and apply it out of context. Wraiths have too low a model count to survive WBB excess...Pariah/TS/Scarabs(etc) don't count toward your totals. C'tan and Monos qualify here too.
Necrons are the easiest army to ignore current objectives (excepting annihilation) and just go for the table, and are the easiest army to table.
I know that yes, you can win games with them..but you cannot consistently win tournament games with adept opponents in an open field with them. They are currently gimped.