Basically, Maribel crushes Leanne in offense during skill usage, but you don't deploy a HA for offense 99% of the time (Skill AW Deine might be an exception), and since Leanne nearly ties her in defense WHILE SHE HAS "Black Tier stats" that means Leanne is clearly viable for tanking a good deal of the content we have. But Kayfabe has a good point in pointing out Leanne's lack of HP can be an issue, so Elva looks like a good option

Leanne at CC50: 1931 HP, 507 Defense, 811 Defense during skill
Elva CC70: 2451 HP, 309 Defense
Elva AW1: 2228 HP, 306 Defense, 459 Defense under 50% HP
Elva: AW 90: 3064 HP, 460 Defense, 690 Defense under 50% HP

Obviously, most Elva users will have her somewhere between 1 and 90 AW lol. Elva gets crushed defensively during skill, without it's pretty even despite the Defense gap due to the HP gap and the AW passive potentially coming into play depending on how much heal support she gets vs. damage incoming. On the other hand, she obviously obliterates Leanne offensively, which means killing whatever is attacking her MUCH sooner without ranged support.

Worth mentioning Leanne's skill won't come into play until 30 seconds after deployment.