There is one way in which Oka favors low XP apt species. Specifically, species which do not evolve by XL. These species are better adapted for diving, because most of their power comes from intrinsic attributes rather than XL and SLs.

Regarding the changes to essential DsNe and BaWr:

DsNe is built for Nemelex, but Nem is not the best god for him pre-Abyss. He starts as a mediocre Necromancer. His weaknesses are HP pool and damage output. His defenses are mediocre and AC is hampered by the need to cast spells. He doesn't start with a weapon, and his weapon aptitudes are -1. When he's caught without skeletons, he can be rather vulnerable against the right opponent.

Makleb balances these weaknesses nicely. Destruction gives a powerful ranged attack. Demonic servants lend teeth to a crowd of skeletons, which tend to draw attacks, helping the demon to last. Servants also provide an ally when no corpses are available. The Regen spell and Makleb's heals on kills give DsNe the endurance to steamroll floors with undead.

DsNe will start wielding shortblades until he finds polearms and staves, and focus on 1h polearms once he finds a shield, with stabbing secondary, depending on his mutations.

I typically skip Vaults:5 until after farming Abyss, since the former can be quite dangerous compared to Depths. Likewise Tomb.

DsNe Makleb burns his piety to earn a quick Geryon kill. Then he switches to Nemelex for Abyss. Makleb is no longer the comprehensive answer to problems that he was in the early game. Linear destruction and demonic summons cannot solve the increasingly complex tactical scenarios that arise. Nemelex is limited by exploration piety, which can be quite restrictive in the corridors of Dungeon. But in Abyss farming Nemelex is trivial. By this time the Ds is much more evolved, and his deity needs are more specialized. Whatever they may be, Nemelex covers it.

BaWr is built for Ru, but Ru is his post-Abyss god, when he is fully trained and tankified, ready to take a beating for Buddha. Ru sacrifices are much more cost-efficient if taken in the mid-to-late game, when skills to be sacrificed are trained up to yield bonus piety.

In the early game, BaWr is vulnerable to swarms due to his slow speed. He can evade with Blink and tank with Shroud as long as his MP holds out, which is not forever. After that, he must walk in combat, which conflicts with his hop cooldown.

Vehumet complements this weakness by providing MP and piety on kills. Veh gives BaWr offensive magic, correcting a glaring weakness. Wr crowd control complements Veh AoE spells. Ba has excellent elemental aptitudes and +1 Conjurations apt. With Veh, he need not depend on his 0 ranged weapon apts, which are low for a Ba. Ba's +1 vision synergizes with Veh's +1 range. Veh ignores Ba's -1 Invo.

This allows BaWr to play his optimal build - a medium-armor spellsword.

BaWr Veh should scum Abyss until he finds and trains Summoning, at which point he can ditch Veh for Ru. A cloud of summoned allies absorbs attacks and repays them with Aura of Power debuffs. Once BaWr's Ru-foo is ready, he can Apocalypse through Vestibule.