Couple things, 11 is a very different game than 14. 14's combat design requires that jobs be able to do the same things amongst their roles. this means, Rune Fencer, Mystic Knight, etc... wouldn't be this vastly different job from the actual melee dps in the game. instead, it'd just be a new flavor of MNK, DRG, SAM, and NIN, that happens to be thematically similar to RDM. 11 didn't have this issue so the comparison can't be made. proof of this claim is that every jobs utilities and kits are all fundamentally similar in this game, all tanks have invuls, all melee have gap closers and weak defensive cds or none at all, Healers kits mirror each other skill for skill except their unique gimmicks, all ranged have a troubadour equivalent. casters are the exception to this and thats only because BLM stubbornly won't get a raise. raise is currently the biggest issue plaguing casters so thats not even a good thing that the role is different in this way. in 11, RDM COULD actually substitute a healer
this means your new spellblader wouldn't be allowed to do alot of what you're hoping it can do and would instead just be another melee dps(we have 4 already) with weak or no defensives and a gap closer as well as a gimmick. the problem now comes in, regardless of how this job feels to play or if this gimmick is fun. If it doesn't do anything, people will perpetually dislike it. Look at SAM as proof and, you're asking for another job that'll invalidate SAM or get invalidated by NIN, DRG, and MNK. it's not worth it imo and, improving RDM seems like the better way of doing this instead of giving the melee dps role 5 jobs when it at best can only have 2 slots. you're also claiming the only way for them to expand on RDM is through magical ranged combat only but thats not entirely true either. they can expand on the melee dps nature of RDM without overstepping it's place as a caster dps by simpling making the melee combo refined and precise, my previous comment mentions a efficient way of adding new melee to RDM without comprising it's position as a ranged.
THe Summoner and Scholar example doesn't apply here very well because these were 2 seperate concept/jobs with nothing alike being tied to one base where as, fundamentally. RDM can easily stand in as the avatar for all other spellblading jobs because spellblader as itself is just a concept, it doesn't imply anything more than magic with a sword. Nobody here has asked for anything unique from this spellblader that RDM can't do, they just want another spellblader. Summoner and Scholar aren't remotely similar in concepts and the devs have openly stated regret in treating them as they did. Im not trying to say red mage monopolizes the spell blade position, im saying, the amount of jobs in this game is getting to become alot and we don't need to add another job to expand on a small concept that RDM can fill.
eventually, this game will have to stop adding new jobs. this holy trinity limitation means that the more jobs we get, the more jobs need to be able to clear content, which intern means more homogenization in what jobs offer. Look at the jobs as they are now, compared to Heavensward especially tanks. nearly pruned dry