To be honest i find this the exact opposite, i just beat a game on endless with vodyani last night - i find vodyani are in a very strong state right now, their arks can be used to extreme effect early game, pushing in minor and major factions alike to where you want them and their snowball potential is out of control. that being said, they are very "do or die", they have a huge falloff if you dont snowball though, a very high risk high reward race, that either you'll find yourself ahead of the curve by lightyears, or struggling just to vie for 2nd to last place

try creating specialized districts, for instance, have your capital ark have 4 dust modules and then you'll be able to handle an army MUCH larger than any ai, even on endless,  and use those massive armies to get huge essence numbers, on normal i find myself with 1000+ essence income by turn 70 consistently which just means massive expansion

i think the key to vodyani is in understanding that they aren't confined to the same restrictions as all other races, their expansion can be as fast or as slow as your essence drawing is, and essence draw is linear (+500 per owned ark, +250 per pop) whereas other things tends to be mulitplicative, meaning their expansion is disgustingly fast if you can abuse it early.

dust is key to victory on vodyani, never use alms for essence, instead, use that massive dust income to support huge fleets of combat capable ships with leech modules, or have a production capital spewing out 4-6 leechers a turn and accepting their losses, also same thing can be done with the black market, selling ships on it for massive profit.

additionally, food income for vodyani is hugely increased compared to other factions, this means the "150" food cost for exotic rations is often less than you'll get in one turn of food, meaning invasion fleets in the rare case that you need them will be extremely easy to bulk up.

and regarding science focused arks, these are the most overpowered, a single ark on a 4x colonizeable system can see upwards of 1500-2000 science income by itself in the midgame, im talking tier 2/3, lol

also as stated in the thread previously, each vodyani pop counts as 1 pop for every colonizeable planet, regardless of size - abuse that, find resource rich planets and get your vodyani arks to 9 pop (you have to level up settlements using the system manager and spending luxury resource), a tier 3 (9 pop) ark on a 4x colonizeable planet will have the effective pop of 36 population, while having the ark module modifers to boot, no other empire in the game can come close to that level of output