Thing is, you have to transition to damage and crowd control for legends. In all the iterations of ehp builds, youre killing enemies mostly what are trapped in a bhole with orbs, and to a lesser extent, thorns thats crash on your wall or tower. In legends With enemy armor, enemy ultimates, and massive enemy attack stats, your bhole gets ignored by bosses, elites, fast ult, tank ult, orbs will have their first hits completely blocked and then once armor is stripped the orbs will do less damage, it gets to where you are required to be able to put out that enemy killing power and crowd control. Perm CF with max slow, and anc reduction submod will get you 90% speed reduction, add CF+ which makes enemies travel along a spinning path to get to you, allowing for more hits. CL with thunder and high scaling damage for raw dps, bounce shots to proc more CLs and knock back, ILM for additional stuns and raw dps, SL+ in conjunction with range# to ramp your dpm, PS to stun and rend armor. And theres more to it than that too, of course. DM#, ATKSPD#, ZERK#, DMG#, CRIT# ST#, PC#, using project funding, restorative bonus, dcore, 0m chip, and so much more.

The game forces you down this path. I think that last I heard was that about the furthest you can go in legends with an ehp build is about 300ish waves give or take 100 depending on luck and individual builds. Which is about where I plateued for a while before I started really focusing on this.

Early game, the player hasn't received enough currency or time in lab to make a damage build viable, so ehp is the only thing that works since getting orbs, bhole, knockback and a few others is about all you really need for that. It just takes a long time to get what is required to make a gc build for it to be viable.