The buss is just a delivery system. It hardly ever does anything at all and if cannons are not present is ran 2 wide with 2 characters a blender lord and baby blender. The banner negates wounds from crumble so my flank protectors hold longer "zombies" and it rerolls frenzy forced charged on vargheists to keep them under control. The vargheists are ran in dart formation with a command upgrade "war machine and wizard hunters or organ gun screen".
Any time the buss is ran wide the opponent simply anvils the lord and attacks the buss. They dont even run a star to do it. an example of a game is when an empire buss charged my buss with cavalry hammers 3 wide 9 models total. He has a 1up 4up lord thrown at my lord. I do 3 wounds with the lord. He attacks the baby vamp doing the 2 wounds and the other character does 3 wounds to the buss. All said and done the buss is now down a baby vamp and 7 knights giving him the chance to counter in his next phase becouse that buss isnt goiing anywhere. 6 griffin knights in his next turn and game over.
Or how about a dwarf lord when your charging you need 5s to hit him and is left with a 6 up armor. With rerolls I pull off 3 hits 3 wounds he gets 1 6 so two more attacks 2 hit 2 wound the lord still lives and 2 wounds make it through with multiple wounds. then anything with a 1up saves on 5+ which is just enough mitigation to do the deed. This is why I am thinking razor standard.
While I don't have the full details seems like there were a few missteps in utilization, rather then construction in these examples. 1st and easiest, the dwarf thing, why get in combat if its dicey? Armor piercing isn't going to change this match up as you negate the non characters saves without it, and a 6 up save for the dwarf is terrible, the loss in maneuverability to negate a 6+ isn't worth it. In this instance, when in doubt don't get in combat, simple,
chaff, avoid, kill warmachines

.
With the empire one few potential issues I see, why did your
blender lord not hit his unit? Even with his lord in base contact you should still be able to target the unit. If he challenged you should have accepted with a champion to allow the
blender lord to well blend

. In this instance 5 attacks from
blender lord, presuming you have quickblood, ogre blade, and red fury you will hit say 4 times, wound say 3 times, reduce his save to a 5+ he saves maybe 1, 2 knights die, with red fury you kill another 1, 3 knights down (and this is with pretty bad rolls). Your baby vampire, kills 2, red furies kills another 1. 4 knights down, 5 left plus the lord? Seems unlikely to loose all that. It also seems like potentially you got out maneuvered since he charged you. A charge during your turn would allow for buffs, which then puts the combat even more in your favor. In this instance, how is armour piercing going to change much? A +1 movement would be much better as its the charge, not the killing power which seems to have worked against you.
Also, against the empire player, seems like would have worked better to reform to having ranks, as you could break his smaller knight bus's steadfast.
Also, as the Sun King has pointed out, the potential for a double
blender lord, especially in a Black Knight Bus build, seems tough to pass up, and would do you much better.
Again, I don't know all the details but these seem like solutions to these problems.