*Laughs in flex*
No, but it's the best blade you can get, at least without sacrificing damage. There's a blade called "Broken Blade of Legends". I'm not sure if it's a legendary blade, because you don't get it in the Challenge dungeon, but, compared to Crimson Blade, you sacrifice 8 Attack to get 17 Defense, 15 M. Attack and 1 M. Defense.... You know what I'm going to equip Broken Blade of Legends, suddenly it doesn't sound so bad to lose 8 Attack. I actually had to type this out to see how good it is, thanks for making that question!
But to directly answer your question "Crimson Blade" is the best Blade you'll get from the Challenge floor, since there are no legendary blades as loot there. At least for now.
It's also good to use in the floor since it reduces fire damage taken.
I just looked it up to make sure, and I found out that there's actually an even better weapon, Purple quality (I think it's Epic quality), called Thunderfury. I don't know its stats, so I'm going to farm until I get it. I'll be sure to send you a reply explaining whether or not this weapon is better than Crimson Blade after I get it. Sit tight buddy!
I'm sorry for the long wait, I farmed for 2 ThunderFuries instead of just 1, to see if they'd do better than a combo with Broken Blade of Legends. I also got the last missing legendary item from the dungeon while farming, but here are my results, after testing in battle in the dungeon.
This is, arguably at least, the best equipment set for Ryen. Although a second Thunderfury gives you 14 more Attack points, aside from the big amount of losses in Defense, M. Attack and M. Defense, your attacks become completely electric, meaning that you deal 0 damage in the fire dungeon, since they're immune to electric type damage.
The Royal Crown may seem a bit odd to be there, but it's stats are actually nice and it gives off a LOT of Luck points. You can change it if you prefer something more defensive though. All other equipped items are legendary, except for Thunderfury, which is Epic, and idk what quality is Broken Blade of Legend, but it has awesome stats, even if it gives just a little bit less Attack than Crimson Blade or Thunderfury. The Attack gap gets shorter as you level up, because it's passive gives 10% in attack, m. Attack, defense and m. Defense, meaning that if you're, let's say, level 100, you'll most likely have a bigger boost from this passive, making it suddenly have better attack stat than any other available blade.
I do however invite @RyenSaotome to drop an opinion on the equipments I chose. Maybe there's an even better blade that isn't obtained in dungeons.
Anyways, to end it, I need to warn you about something. Farming for a specific Epic equipment is SO MUCH HARDER than farming for specific Legendaries. This is because Legendaries are unique and won't drop again, while most epic items aren't unique so you run the risk of getting a lot of repeated Epic quality equipment before getting the one you wish for.
Now imagine me farming for 2 ThunderFuries XD. I could've hit level 75 but instead I relied on autosave, which saved the game right before fighting the dungeon bosses, with red chest available. It saves time but since I'm always loading the game I'm sacrificing Exp gains.
Sorry for long post, good luck farming!