Is heavy merging needed for tier 20 arena

I'm at tier 18 without having merged units. I havent gotten into 19 because I never have the bonus heroes for that time frame. And that puts me back down to 17, then i go back up to 18, and then hey guess what still no bonus heroes for this season so back to 17 i go.

to stay in tier 20, yes

Heavy merging isn't required to get into Tier 20 since scores of about 696 and up can get you in. Staying in Tier 20 is the hard part, needing about 720 scores per battle to edge out top 5,000. The only reliable way to hit scores this high is to use merged units.

If you're looking for things to invest into, one thing you'll want to have done is have your original Askr Trio (Alfonse, Sharena, Anna) up to 5. It's a hefty cost, but this will always guarantee you have a bonus unit for every arena season as the last bonus unit is always one of those three or Fjorm. The best units to supermerge are units that can be summoned at both 3 and 4 star rarities, but you can merge units that only appear at 4 star rarity, although it will take a bit longer. There are certainly very good units laying down in the 3 star pool, so don't be afraid to dig them up. Here's some personal recommendations in the 3 star pool that will serve you well when built correctly.

Red: Draug, Hana, Laslow, Lon'Qu, Olivia, Palla, Selena, Sophia, Tiki.
Blue: Donnel, Est, Gwendolyn, Oboro, Shanna, Subaki, Robin, F!Corrin
Green: Barst, Bartre, Beruka, Cherche, Nino.
(You can use horses or colorless too, but they generally score lower.)

Good luck!

Getting to T20 is easily done with non-merged units so long as a couple of them are Melee units; a team of unmerged mages, for example, would be tricky to pull off for T20. I have minimal merging on my core arena team(one +6 mage and a bunch of unmerged or +1 merges I rotate through as needed) and I've been in T19.5 for a long time (bouncing between T20 and T19 every week). Not running a dragon or armor emblem either so we're working with standard BSTs.

But yeah, totally doable. I don't think it's possible to stay in T20 without DECENT merging; I don't think you need +10s for everyone, but you'd probably need at least 3 around +5, I'd assume.

To get in? Nah, just throw +2 on a couple units

To stay? Absolutely; everyone on ur team needs to be +10.

Bc u know what’s in T20?? 5*+10 Amelia’s and 5*+10 Ayras. *whale noises in background*