I noticed you only count the crit part of LotP, but the heal part of ILotP is a non trivial aggro boost.
If you have 20 000 hp, the heal from IlotP is 800.
On average you should hit 4 specials each 6s (with SS, rev, dev, dev cycle) + 2 to 4 white hits (1.5 to 3.0 auto timer). Let's say totally 6 hits each 6s on average, with a 16% crit rate one should be a crit granting you a 800HP heal.
Heal aggro is 0.5 per heal : 800hp heal x0.5 x1.45 (def + defiance) = 580 threat per 6s, that's 96 TPS.
Of course this only occure if you crit one time each 6s exactly, but with ILotP limited to one proc each 6s and only 16% crit rate you cannot be sure to have a heal each 6s. Unfortunatley I have absolutly no idea how you can calculate this more accurately
However, I think ILotP should be added if you can as it could be a big part of threat.