A very fine linestage will usually improve tone and dynamics vs. running a source (in this case the phono pre + cartridge sourcde plus preliminary gain) even though with a linestage you are usually throwing away some of the system gain. But sometimes the right combination of phone pre + power amp can deliver sound that argues for eschewing the preamplifier.
Two things are critical: First as already mentioned by others, somewhere you need a volume control. The second is often overlooked in the gain chain: the input sensitivity of the power amplifier vs. the maximum clean output voltage of the source, before clipping.
Something an Audion power amp with 0.7v input sensitivity can be driven to full power without strain or dynamic clipping by almost any source (including the output of a phone preamp, but not including the output of a cartridge directly) without the extra boost of a preamp in the chain. On the other hand, some American power amps that have input sensitivity of 2v, 2.5v or more can't be driven to full power by the output signal of a source only able to output less before clipping. And an output spec of 2v isn't a guarantee that the analog output will sound best when operated at its limit. So get that relationship right, and you will at least not be shortchanging your power amp's available dynamic range, nor pushing your source's output into compression or clipping. Whether a preamp sounds tonally better in that case over no preamp, is up to you to decide for yourself.