The Sun EZ-1 is not a particularly fast bike. It has small wheels and an upright seating position, so the aerodynamics are probably not much better than an upright bike, the (small diameter, moderate-pressure) tires have a lot of rolling resistance, and the EZ-1 is almost certainly heavier than most typical uprights at the same price point. So yea, it was probably slower.

Better (fatter + higher-pressure) tires can help but there's not much you can do about the upright riding position or the overall weight. While the seat back is adjustable, if you recline it too much you cannot push against it to pedal very hard.

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With most upright bikes, there's generally not a lot of variation in riding position or overall design, so how fast they are mostly comes down to weight.

With recumbents you have much larger variations in rider position, wheel sizes and weight. Most recumbents that have you sitting upright are easiest to ride and are very comfortable in pretty much all riding conditions, but they aren't ever fast without fairings or other aerodynamic add-ons. People buy these bikes just for the comfort provided.

If you wanted a recumbent that is fast 'naked', you have to buy one that is intended to be fast (that is, that has the rider in a steeply-reclined riding position).

The Bachetta Strada and Volae Club are two "stick bikes" that are relatively light & fast (both around $2000).

The RANS X-stream is a fast long-wheelbase with dual 650 wheels, for $2700.

Both of the above are bikes with 650c wheels, with a "sit-over" height pretty far off the ground. For shorter riders, the Catrike Musashi is a midracer that is built lower to the ground, and goes for around $2400.