that is true about the weapons.
strongly advise putting the same combo on your lord. the black mace is garbage if it's not on a daemon prince. even against orks you've got to expect that your lord will run into 2+ armour. if he can't deal with it, it'll hurt.
if you can get a copy of the Crimson Slaughter detachment you can look at some wargear on your lord I love using
Daemonheart - 2+ armour, plus it will not die
Slaughterers Horns - rage and furious charge
Special Sword (cant remember the name) - gets buffed as he kills stuff. fun sword, claw and fist are probably better though.
psyker level will be doable. generate a few dice with the warp roll. get 2 from the herald. need 3 success. throw everything at it and keep summong plaguebearers.
here's some notes
Lord - give him better wargear, fist and claw is good or use crimson slaughter stuff
Bikes - take double melta. you're really lacking it. probably dont need the fist and claw on the champion. take the fist only if you want more punch.
Plague marines in a rhino with 2 melta is always good. i run that a lot. get melta.
I would Drop the plague marine squads with no rhinos. maybe take 7 guys in the 2 rhino squads. no rhino and they're a waste of time. free up some points for elsewhere.
Herald - locus is a waste of time unless he's in a good unit. a unit of 10 plague bearers doesn't need feel no pain. won't make your points back.
on the other hand, if you drop the extra plague marines and take 20 plague bearers with their shrouded and feel no pain you will have a unit that's basically impossible to move off of an objective. it will also have enough attacks to kill tanks that get too close etc.
soul grinder is always fun. phlegm is good. gives you a bit of skyfire too.
make those subtle tweaks and you'd have a decent list for friendly but competitive games.
lord and bikes turbo forward on turn 1 and then drop melta into something. maybe the lord even splits off to fight on his own while the bikes melta something else etc.
two plague marine rhinos with melta follow them up with turbo. when the rhinos get popped the marines will be in better position to melta slag something and then get into a fight. plague marines are pretty solid in close combat. theyre tough, hard to kill, hard to wound and have lots of attacks. against orks and astra youll also be rerolling your failed wounds in combat due to poison. dont forget that.
big plague bearer unit can sit back and score and not move. soul grinder can hang back and shoot a few things.
if you want more punch look into a squad of about 6 plague drones and put your herald with them. THEN the fecundity makes sense. they can really hit like a ton of bricks. i also use a big nurgle beast star at tournaments and it does well.
look at epidimius if you're using lots of nurgle daemons. he can be a lot of fun.
a nurgle daemon prince from the daemons book can take a balesword. fly around and jink for a 2+ cover save and then charge big nasty targets with an instant-death sword.
a great unclean one with a couple of good biomancy rolls ends up being T10 and basically impossible to kill. as a nurgle player i take an unclean one and a prince all the time. 2 greater rewards on each and 3 rolls on biomancy. youll get solid powers more often than not and all of the greater gifts are good. you can either take the balesword or the etherblade for +1s if you dont really need
ID because your opponent doesnt have multiwounds.
if you really want to take a blackmace then take a daemonprince so it's at ap2. that can really hurt.