The unit has between +3 and +5 extra attack vs most units (vs kts it's +5), additionally it can have up to +5 attack from relics (+1 from each relic) and the elite version has the same base attack as a paladin.
If you have an elite leitis vs a palain it could have up to 14+9 attack (with all 5 relics), which would ignore armor, so it's actually like a paladin with 14+14 attack (just insane). While a FU spanish paladin would need 12 hits to kill one FU leitis, the FU leithis only needs 8 hits (!!) to kill the paladin, means it hard counters paladins. Just to compare: an FU imperial camel needs 7 hits, but hits slower than a leitis, so leitis are more or less like imperial camels vs paladins, if you gather 5 relics.
If you only gathered 2 relics, you have 14+6 attack, which corresponds to an actual attack of 14+12. Then a leitis would need 9 hits to kill a paladin, which is still incredible fast.
Now the major difference between impcamels and leitis is: leitis perform better vs ranged units and much, much better vs halbs. In fact if you gather 2 relics, you have 14+6=20 attack, that means you need 3 hits to kill a FU halb. A FU spanish paladin would need 4 hits to kill a halb.
Now how likely is that case where you have 5 relics? well in 1v1s it's unlikely, but in TGs collecting 5 relics is now not that unlikely, since the rated standard maps now have more relics than before (I counted 8 on ghostlake yesterday).
Leitis really need some nerf, atm they are as uncounterable as imp camels before the nerf (if not worse). Personally i would like to see that they remove the last cav armor up from lituanians, that would make their cavalry at least counterable with ranged units, since halbs/camels barely work.
Well, you are not being fair in your analysis.
You can believe that the relic bonus is OP (I think it is very good, not sure if OP) and it has nothing to do with leitis.
I mean: why should anyone make leitis instead of cav/paladin? They both get the relic bonus, so you cannot take it into account. Knights do not require a castle and they are cheaper for their stats if I am not mistaken (cannot check it out right now)
About the steppe lancer, it is clear that they will nerf it probably this week, I only regret thatbI wont have time to check how OP they are