A short foreword:
Legionnaire is one of the most conceptually unique heroes, unable to be truly classified into a singular role regardless of item or skill build. He is, almost unquestionably, the most simple and reliant initiator at all stages in the game in the context that he has a superior magic disable combined with naturally scaling tanking ability. But Unfortunately, he falls short in the naturally assumed idea that he requires farm equivalent of Hard Carry but cannot perform as an actual hard carry.
This brief strategy guide is an attempt at removing the stigma of the counter-productive build of Contemporary Legionnaire and indoctrinate the idea of a much more support oriented Legionnaire that can play an effective role past the mid-game.
This guide assumes you understand the Basicís of Legionnaire, because instead of analysing the raw skill I will provide rational into the levelling of each individual skill under subjective conditions.
Neither skill has direct preference over the other, due to the intended synergy behind them. The Brilliance of this is that either skill is still effective to a degree when the opposite skill is left at level 1. I recommend that you choose a skill to max first based on what the team is in need of, simply put ; Taunt for lack of early disables or Whirling Blade for lack of early damage. Keep in mind that regardless of condition, Whirling Blade should always be taken at Level 1.
There are 2 options to approach when levelling Terrifying charge. The first option being to level it once early for pure jungling purposes and minimal usage for mobility until acquiring Portal Key, the second option being to Max it as a secondary ability between the distribution of Taunt and Whirling Blade, essentially using it much more combatively in ganks. And please, NEVER choose stats over extra points in terrifying charge.
This skill will always take levelling preference, since there is no reason to avoid it. In relation to the kill stealing stigma, it is just a matter of using it selectively and at the opportune times.
Depending on your choice or the given scenario, your levelling choices should look like one of these three options.
[Skill trees go here]
Since your farm ability is unparalleled at almost all stages in the game, but your inability to efficiently be maintained as an item Dependant carry, then why not go a support route into the mid game?
I have found that acquiring a :Portalkey: :PlatedGreaves: :HelmOfTheBlackLegio :RingOfTheTeacher: by the ~28 minute mark is a fairly achievable goal if you manage to farm effectively in jungle and assist in a handful of ganks.
These Items are the crux to make Legionnaire efficient in tanking without becoming too dependent on farm. Helm provides the neccesity of Health and damage block, and Plated combined with Ring provide an excellent +8 armour which...
After this, a :Puzzlebox: becomes an absolute neccesity in my playstyle, as it provides unquestionably highest damage ratio during the 3 seconds of Taunt (when placed in the context of achievable items). It baffles me to think how overlooked Puzzlebox's potential on Legionnaire is, considering he has a 3 second disable that forces enemies to stay at the prime distance for Pbox minions and the fact it provides Legionnaire with a secondary burst damage skill to bring that juicy threshold even closer. And assuming you have caught the enemies pants down with a nice blink combo, they will either be dead from a wizard nuke->decapitate combo or have a heavily reduced mana pool to retaliate with.
Lategame Is very dependent on the line-up's and scenario, but I tend to find that aemonicBreastplate and :AbyssalSkull: provide the most useful output considering they are the best tank/support items and provide Legionnaire with higher presence and impact on the teamfight. Items like Behemoths Heart are pure greed items and provide no input to Legionnaire's initiation, they only help him stay around a little longer.