Tell me if i'm wrong but at this speed it is still not profitable, am i right ?
Depends... when 580 can do 22 and 1060 does 26 - they are not too far appart ... same as with 33 (vega 56) vs 1070 speed.
Atn mining is not that profitable it used to be half a year ago with prizes up, but at new versions sol/s it should be profitable - of cause depends on coin and energy price.
Do you have api support and zergpool stratum?
The miner has a simple api. Zergpool stratum? Whats different there?
Lolliedieb good job!
Is it still possible to increase hashrate?
Of cause its almost always possible, but the jump will not be so big again. Maybe 2 to 3 sol/s on top for 144/5? Ok, maybe more but as with every trick the dev has to find it first

For me with my 2 RX 580 change is:
14.5 each to 20 sol/s (+38%)
Go this way, when it reaches 100 sol/s per card it will be profitable

Thats odd - before yours was much faster, now slower. Hmm ... most changes targeted the memory controller, maybe different vendor of mem chips?
My testing gpu is a saphire pulse 4g at stock clocks, what is yours?