The largest gap I have experienced is just lv10, so my words might not count as a real answer…
Since I chose Swordsman2 instead of Peltasta, when I have to tank bosses, all I can do is first draw bosses’ attention by using damaging skills, then read the attacks and dodge it. If there is a chance to attack, just do normal attacks, whose function is only to keep bosses’ attention on me. I find this method is less likely to make mistakes, whether they are due to my own fault or the low latency or whatsoever. And this is very important when tanking 10 level higher bosses, coz one mistake is an instant death for me 
It won’t be too difficult if my teammates are willing to deal one boss at a time. To tank both poata and mole is just a pain in the ass even when their level are lower. The combination of poata & tree is not too scary tho.