It's all subject to the relative qualities of each; but yes, in general and for the same amount spent an amplifier and pair of speakers will give a fuller and higher-fidelity reproduction than a sound bar. Part of the reason is driver size.
A typical soundbar has evolved to fit in to the narrow space created by the height of a table stand. Naturally then, that limits the size of the speaker drivers that can fit. Circular drivers are limited to a diameter of 1-1.5". The lowest frequencies they'll go to is 100Hz, but in reality the lowest useable range 120Hz. Oval-shaped drivers can offer some advantages in bass extension if carefully designed because of the larger cone area. This does push up the cost though, and since cost is king when it comes to typical mass-market consumer-product design then you won't find the best quality oval drivers in sub-£200 sound bar. That's why you'll often find subs being used to supplement the midrange and bass. It's a bit of a juggling act though for a manufacturer. Spending money to make a sub means taking it away from the budget for the sound bar.
The performance gap does narrow as budget increases. Get past the £500 threshold and choose a sound bar or sound-base with relatively-large drivers and you'll find it will produce pretty good music performance, so the limitation is mostly down to form factor. The Sonos Playbar, Yamaha YSP-range and Naim MuSo all spring to mind. They're all chunky devices and sound so-much-the-better for it. Something similar but on a smaller scale happens lower down the price ranges. The Q Acoustics M4 is taller than your average Sony/Samsung/LG soundbar for £200, but you can hear the difference that the bigger drivers make.
Strictly-speaking, the MuSo isn't a sound-base, it's a table-top streaming music system, but the line inputs allow a TV connection and it's really rather good.
Coming back down to more wallet-friendly budgets, a good stereo amp (Onkyo A9010 - £199) combined with some good bookshelf speakers (Wharfedale 220 @ £99) will produce a very musical system; and if a system does well with music then it'll do equally well with TV sound.
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