Why so many Distant Def users?

The thing is, most of the major threats in arena are ranged, Reinhart and B!Lyn being two of the biggest. Distant Def effectively gives 12 more HP against these foes, which is huge. Additionally, it can add ~3-5 damage to specials, once again, huge.

Melee is very easy to bait and win with color advantage or range, but ranged baiting may require using a unit that does not have triangle advantage. Distant def just helps make that baiting easier.

There's so many Distant Defense users because Distant Defense is just that good of a skill. A skill that adds Def/Res when attacked against Bows, Daggers, Magic, or Staff? It's an amazing skill that can benefit a lot of units, so it's pretty easy to see 'why' it's used so many times.

As for Speed +3...that's not used as often because there are simply better seals depending on the situation. Not gonna put a Speed +3 seal (mine's not even max'd I don't think) on a unit when I can give them something more bulk, attack power, less special charge time, debuffs for enemies/buffs for allies, etc.

'+3' seals aren't bad, they're just simply not used because of better seals in a lot more situations.

The +3 (+5 health) and QP seals were great at first. Unfortunately, they have like 100~120 arena weight I think. Distant/Close Def is essentially a free +6 def and res, depending on how they want that unit to play (melee or ranged/distant counter) and gives 240 arena score.
Ranged units are almost 100% expected. They threaten more of the map than any other unit, hit hard, are fast, and are less susceptible to counter attack. Almost all viable melee builds run DC or have it built in.
If you dont have units readily available like B! Ike or Fae that can handle B! Lyn and/or Rein, or any other ranged, (and even they need Distant def), you have to use Distant def on someone or else they single handedly can easily pick off a unit and run down your entire team.

+3spd and atk Seal are still fine and good for main nuke Heroes still +3spd can be used as a defensiv Seal too..
Most Players using atleast 1 lure Hero and Distant Defense is just way to strong to pass.
Like you said and agree must say is it bad on Ike(still maybe better then nothing if you have no good lure Hero) this Seal just be rather be used on example above you said or other good defense res Heroes like Nowi Fae as example
We will see now more players with QR soon in Arena because it is just a insane Seal.
Ike became way to weak w8ing actually for a Weapon buff for him or maybe they bring now a powercreep Ike because of Zelgius^^

Brave weapons have fallen short. They have no upgrades, giving them very little potential and terrible versatility, so deflect seals are pretty useless. Arden is almost non-existent and Rain has a million counters. Even Amiti isn't common since flyer emblems are arguably the most expensive to build.

The people who have the highest arena rating don't use ranged units often. I get 750 points off of teams using Gunthra, or W!Tharja, though beyond that, end game ranged units are rare.

However, choosing the hardest teams in arenas means that you're likely to fight teams with fewer ranged, but your lower rating means you're more likely to use them. So from an arena defense perspective it's a good idea. Tempest trials are easy, and baiting is much more simple, so it's a good seal to use then as well.