Your core problem is damage. It might seem like your EOIV party but Landy's aren't as offensive without a lot of work and Survivalists will never rival a Sniper. Your troubadours offensive buffs won't do much for a relatively weak party.

Before giving advice it's important to talk about the grimoire system. To get another classes skills you must first level up that class high enough to get the skill and pass it onto a grimoire. So if you want a healing troubadour with some heals status/bind heals you need to first level up a medic and grind out those grimoires. You can get a small heal and ae heal from the protector but that likely won't be enough unless you rely on items for statuses, binds, revives, etc... That's a huge pain in the ass.

So it's important to plan your party around how much grinding you want to do since getting grimoires is a pain. If nobody in your party naturally has an ability and it's not available from an early grimoire then you will need to raise an extra character just for that skill. Keep that in mind when planning.

Landy's are late bloomers when it comes to damage. Their basic sword/axe skills are decent, but nothing special. Getting the elemental chases takes a lot of investment for both the landy AND getting your casters some multi hit enemy grimoire spells. There aren't any single target multi hit elemental attacks you can get naturally. They're solid tanks though and can substitute for a protector. Their buff triple charge is great for other classes.

Survivalists is a weak damage class. They start out decent enough but are quickly outclassed. Nice utility, poor damage. I used mine mostly just to get some gathering grimoires...

Alchemist is extremely useful. Once you get Focus leveled up a bit you can really start spamming magic. Perhaps not required, but still extremely good. Goes well with a Landy if you pick up the multi hit enemy skills.

Ronin are somewhat fragile, but Swallow Strike is extremely good. Moreso if you use it with the Landy's triple charge. That extra accuracy really helps and triple charge helps offset swallow's high tp cost. The elemental skills are also great for slash resistant enemies and groups. One thing to keep in mind is that their stances count as a buff, as does triple charge. With the 3 buff limit be careful not to knock stuff off with your troubadour and protector.

Troubadour as a healer in a game without subclasses means you must first raise a healer to a high enough level to get those healing spells onto grimoires. A medic is the only way to get those AE status/bind heals and the big single target heal. You'll also want to get a focus grimoire on them to help recover TP.

Medics are somewhat of a necessary evil if only to get their skills onto grimoires. On the flipside you can also put other grimoires onto them. You can give them some attack magic or buff skills and get a well rounded character.

Now, when i planned my party I did it knowing a bit about the grimoire system and lack of sub classing. I heavily favored a lack of grinding. So I went Landy/Ronin/Medic/Alch/Surv. Once I got some gathering grimoires I swapped the surv out for a hexer although any damage or utility class would work. This group had everything I needed in terms of tanking and healing. I was able to give the medic and hexer some attack magic. I was able to give the hexer a high level focus for tp regen. I could give the ronin triple charge and def up from the landy. I could give the hexer some healing from the medic. I could give the medic/alch/hexer some multi hit spells to get the Landy's chases going. Overall it worked pretty well in that I didn't need to really grind grimoires and I got everything I needed naturally.