The big uns upgrade in the new book is too cost efficient (+1S and +1 WS from initial S3 and WS3 often significantly increases the hit rate and wound rate and can often reduce the rate of getting hit) to ignore most of the time and you get the most bang for the buck with it by having an AHW most of the time because it doubles the value of the upgraded attacks in the front rank. But the big uns upgrade is most efficient for savage orcs because they get a 6+ ward save and extra attacks with frenzy. Savage orcs are the most points efficient core unit of orcs. If you want a tar pit, then night goblins with nets and shields are most efficient.
There is always a debate between more protection and more killy, but generally the rule in 8th edition is to maximize the ability to kill. For example, chaos marauders with great weapons are superior to HW/S as long as enough models are run in the unit to survive after the enemy strikes first. Similarly, a grave guard unit whit GW is superior to with hand weapon/S but you have to run the unit a lot larger to be effective precisely because it is less resiliant and striking last. If you are going to run a unit smaller with characters, then marauders with MoTz and HW/SH makes more sense and the same is true with HW/SH for grave guard. The same rule appllies to ordinary orcs. If your unit is getting whittled down, then you are matching it up with something superior such that you need to increase the size of the unit, figure out how to deploy and move to obtain more favourable matchup, or accept that the unit needs to kill enough to make back its points before it dies (including so weakening a superior unit so as to allow additional units in your army to ultimately finish off that unit).