This is the crux of Jund's weakness against combo: Jund can absolutely prevent the initial combo attempt, but its clock is pretty slow
Ruby/Sapphire Starter Deck List Improvements + Cards To Drop Most cards with Support or healing abilities on their own should go
In her Planeswalker form, Tamiyo boasts a suite of powerful abilities, culminating in an ultimate that draws half your library
Flying and mobilize 2 let it pump your team, and when it enters, every creature you control permanently gains menace, lifelink, or hasteyour choice
Slaughter Pact and more are out there, but not really as good when you could be using blue
A spell cast using jump-start will always be exiled afterward, whether it resolves, it's countered, or it leaves the stack in some other way