WEAPONS ARE FOR PUSSIES vs DO NOT PURSUE
They both fill the same niche, which is to say single target Berserker with Buster NP. So lets see just how good did Lu Bu become with these new buffs using Beowulf as benchmark.
Base stats: As 4*, Beowulf has around 2k more in each stat. He has one more hit on Quick and Arts, and twelve hits on his NP compared to Lu Bu's 1. Lu Bu has better NP gain though, even with his lesser amount of hits, as well as smaller death rate, and 5 less cost due him being a 3*. Lu Bu is Man while Beowulf is Earth, and i believe that Man is generally better due less Sky types, but i can't be arsed to check.
Defense: As mentioned before, Beowulf edges out Lu Bu by 2k, with one having slightly above 10k while other sits slightly above 8k. Lu Bu can actually make himself slightly tankier with his 15~25% defense buff, but taking in consideration its downside, limited time and fact that Beowulf has Battle Continuation B, Beowulf takes this, although not by large margin.
Attack: Again 8k vs 10k. Both have similar attack buffs, with Beowulf's being better at start, ranging from 20 to 30% while Lu Bu's is 9~27%. Lu Bu's does give him mental debuff resistance, but that's fucking irrelevant. Beowulf does have Instinct B, but his 4-14 stars are kinda minor. Big thing is Lu Bu's recent buff, allowing him to reliably collect stars. Indeed, with his attack buff he hits about as hard as Lancelot with his NP buff, making him force to be reckoned with. Not only that, but Lu Bu gets 10% bonus from his passive against only 1% Beowulf gets, which really cuts on stat lead Beowulf has on basic attacks. Indeed, i would actually give advantage to Lu Bu, as he has slightly lower attack usually, but way higher spikes and it's pretty easy to set them with Saber outfit.
NP: As mentioned before, Lu Bu can build it a bit easier. His crits don't actually help, as you want to use them with his Buster. Their stats/passive from above still apply, but Lu Bu's straight up better NP dmg up skill(20~30% vs 10~20) lets him completely close the gap between the two. Beowulf did have a NP upgrade Interlude which Lu Bu lacks, meaning +100% NP damage on each level, but as 3*, Lu Bu is way easier to max out. Beowulf's effect is crit chance down, which is relatively useless, while Lu Bu's stun, although low chance(furthurer rekt by debuff ress), could really come in handy. Due ease of acquisition of additional NP levels, i'd give this Lu Bu.
Verdict: Despite Beowulf's base stat advantage, Lu Bu's better skills, passives and NP make him comparable to him, if not actually better. While fiddly to play, between hit 3 turn 50% to not get attack up and 20% def down for entire part for one turn, Lu Bu is pretty damn strong when you get a hang of it. Needless to say, he makes other 3* Bersekers look inadequate in comparison.
Either way, it is undeniable that Lu Bu is in extremely good spot right about now, especially with his 3* cost giving you more options to play with. And with possibility of him receiving Interlude buff to make him even better, you should really consider droping some EXP and Fous onto the big boy, especially if you happen to lack gold Berserker.