Not true. You can easily get an archmagi item (devils area belt) and a greensteel sp boost mod to encorporate along with mental toughness and improved mental toughness (since your a fighter you will have a lot of feats to pick). If you are dedicated, you can farm a bauble from weapon shipment to have a clickie renew sp item (since it does 300-500 sp renewal) You will be in the 300-400 range. I am not saying it is better or worse than a pure lvl 20 elf ranger, but if your going to go with a lvl 18 fighter, you might as well go 20 and get the fighter capstone and an extra feat.
And yes, the Kensai feats do add up to be quite nice. Surge and the +1 crit range is pretty good. I may reroll one of my lvl 20 AA's into a sorc and then into a pure lvl 20 fighter. If i don't like, he goes back to lvl 20 ranger.