Level 10 Magical Secrets - Lore Bard in Princes of the Apocalypse

[Chaos Jackal]

Conjure animals/woodland beings are crazy if you get to pick the summons and the former is generally good even with some limitations.

Wall of force might be shared with the wizard, but the power of the spell cannot be overstated. Multiple people with wall of force aren't redundant, they're just that much better together. You can pretty much control any encounter with two or three of them.

Circle of power is a very good paladin exclusive (unless your cleric's Twilight) that you get many levels early instead and is universally good. Becomes even better depending on what your DM considers a magical effect.

Summon celestial is a good controllable summon with a lot of DPR and utility (it heals and you can ride it).

Find greater steed is admittedly less useful in narrow corridors and small rooms and I'm not very familiar with PotA's structure, so if you say it's not favorable I'll take your word for it. Still, worth a mention.

While we're talking lower level spells, pass without trace is often free surprise and a good way to let you avoid encounters you don't wanna bother with as well as an excellent scouting tool.

Finally, if you are OK with potential moral implications and can convince your party it's not actually dangerous (it isn't if you place it well), there's always summon greater demon. It's stronger than any TCE spell and unlike the mass conjurations you are explicitly allowed to choose the creature yourself; babaus, barlguras, tlacatecolos, shadow demons, stuff like chasmes and vrocks if you upcast, make for a really good selection that is strong, tough and offers a lot of utility.