The question of the topic wasn't about whether their self sustain options are dps minus to use improperly - the question is which melee dps can keep itself alive the most when playing solo, content that by nature, will matter much less about playing optimally rotation wise. Which yes, Life Surge is an incredibly strong infusion of HP when used with your strongest potency skills with the added bonus of being able to stack 2 charges of it.
Also, the heal from life surge is hardly 'almost cosmetic'. Looking at Whoop's first clear of P8s on week 1, he had about 70k HP, and it healed about 4k on a non-burst phase heaven's thrust, a little over 5% of his total HP. For contrast, a SAM would have to get hit by an attack over 40k damage in order for third eye to match it, or a MNK would have to get hit by at least 20k damage during RoE for them to match it. That's also non Litany/DS/Lance charge, with those buffs factored in Life surge was healing Whoops closer to 8k damage, more than Arcane Crest shields for.
Also the maiming sets do in fact have better HP - you can verify this trivially easy by looking at the BiS sets for each. Now that being said, it is only 700 Hp difference, but it is still a positive for RPR / DRG nonetheless. Also another factor to keep in mind is that the maiming set all pieces combined has about 700 more physical defense than the striking does, which translates to an extra 3-4% passive physical damage reduction, meaning Riddle of Earth's effective gains are reduced further comparatively.
As far as the topic, which melee can keep itself alive is dependent heavily on context:
MNK has an extremely beefy 20% mitigation on Riddle of Earth, but if its just only ever fighting a single enemy that deals relatively low damage over a long period of time but would be guaranteed to kill the MNK with enough time, Riddle of Earth's effectiveness falls off the face of the earth compared to direct healing, since % mitigators more shine in high damage or rapid damage instances. 20% off an enemy hitting you for 2-3k damage per hit is basically useless compared to a RPR shield blocking 7k HP within that same span. MNK however, does get the benefit of a very meaty bloodbath if it lines up with their burst.
RPR's shield provides a flat 7k-ish barrier each use which makes them incredibly powerful against single targets or low incoming damage scenarios.
SAM's third eye is basically a non-factor since it only mitigates a single hit, SAM however does capitalize on bloodbath super well due to how strong their upfront potencies on their combo strings are, along with extremely high damage potential during their burst windows due to auto CRT Midare/Onigikiri
DRG gets life surge as an additional self heal with the bonus of 2-charges on top of it, leading to a lot of extra healing throughput compared to the others.
NIN is arguably the worst. I think part of its burst is technically magic damage which doesn't work with bloodbath, along with its barrier being once every two minutes compared to the other job's much lower CDs.
I'd say overall, RPR is the most versatile at keeping itself alive. RPR's high combo potencies along with Enshroud burst synergies well with bloodbath, and Arcane Circle is a meaty 7k-ish barrier every 30s with a possible 250 potency worth of healing afterward. MNK would keep itself alive longest in crowds or in high damage scenarios due to % mitigators working the best with high amounts of incoming damage. SAM & DRG would both work best in slow war of attrition middle tier damage scenario where direct healing dwarfs both barriers and % mitigators. NIN is basically bottom regardless of situation.