That's not how they are presented in the 5e books.
Or, if it's like a SW game, it's Old Republic SW, where anyone can play a jedi.
Can you realize that that's not what we're arguing? We get that! What we're saying is that we prefer the old way!
The way it is now, the very fiction of the game itself is altered because now, all spellcasters are guaranteed to be "Greater Marked", while all martials are locked out. This throws a wrench into the internal fiction of a few of the houses, most notable House Deneith, the mercenary/bodyguard house. Have it from Anthony Turco, author of the Adventurer's Almanac, one of the best DM's Guild supplements for Eberron:
[11:41 PM] NovaSeaker: From their earliest conception, dragonmarks grew in size and complexity and granted more potent magical powers the greater the mark was
[11:41 PM] NovaSeaker: A staff or rod that lets you cast spells tied to your mark is great
[11:42 PM] NovaSeaker: But it doesn't convey the same prestige and significance as being the bearer of a Greater Dragonmark
[11:43 PM] NovaSeaker: You didn't need to learn to use the mark before. As you grew in ability and significance, so did your mark.
[11:44 PM] NovaSeaker: Also, let's be real, it's not like we have to take the Fighter down any more pegs
[11:44 PM] NovaSeaker: There's no reason whatsoever to thumb our noses at them
[11:45 PM] NovaSeaker: Taking a feat can also be just as much a sign of training, if you like
[11:46 PM] NovaSeaker: Picking up a staff and attuning to it, much less so
[11:47 PM] NovaSeaker: Also, in lore, House Deneith's heirs with the Greater Mark of the Sentinel should be world class fighters
[11:47 PM] NovaSeaker: Not wizards
11:48 PM] NovaSeaker: Blademarks and Sentinel Marshals aren't known for their spellcasting expertise
[11:48 PM] NovaSeaker: Not exactly
[11:49 PM] NovaSeaker: EK can't cast 5th level spells, and it only gets 4th at insanely high levels for Eberron
[11:50 PM] NovaSeaker: So to get like, moderate magical power from the mark, you need to be the single most badass swordsman to live in a century
[11:50 PM] NovaSeaker: Not exactly filling the ranks of the Blademarks
[11:53 PM] NovaSeaker: Deneith hiers should be capable of casting the 5th level spells of their mark when they're of a level to be of notable skill, but not a hero out of legend. They regularly put a price on the services of such heirs