When used properly and in the correct amounts to the needs of your tank/plants liquid carbon is not a waste of money. I ran a high tech- high light tank for over a year using liquid carbon. The only reason I didn't have a problem and got such good plant growth is because I used liquid carbon at the proper amounts. I also have low light tanks that I use liquid carbon in that have medium light plants growing in them which wouldn't work if I wasn't dosing liquid carbon. It is not a one dose fits all tanks product. And when used in proper amounts daily it aids plants in photosynthesis and growth. Plus you can buy Metricide 14 day solution, a gallon for $20, dilute it at a 1:1 ratio with RO or distilled water which gives you a slightly stronger solution of Glut than what is in Excel, and you end up with 2 gallons for roughly $27 including shipping. It's very cost effective.
As already asked you need to post exactly what lighting your using and the type of bulbs. Also how long daily your running them. When having algae issues you should only run lights 6 hours daily until you figure out what is causing the algae and the problem is correct and algae is gone. Also what you consider 'adequate' lighting may in fact not even be remotely enough for the plants your trying to grow.
So basically if lighting isn't suited to the type of plants being grown and not enough of the proper micro and macro nutrients aren't being supplied along with no CO2 or liquid carbon plant growth is going to be very very slow and if not enough light plants can eventually just waste away. If your having trouble with your sword you most likely aren't supplying enough nutrients (enough root tabs often enough). They are very heavy root feeders.