Do subwoofers really help?

I would hesitate to suggest that a subwoofer can cure a 'mismatch' between amp and speakers. It's really only when your amp and speakers are as perfectly matched to each other as possible, that subwoofers can add that extra dimension of low-end foundation whilst seamlessly blending with your existing speakers.
The priority in my experience is to find the 'best' possible speakers for your listening room regardless of the amplifier/s. This is the 'key' to overall eventual satisfaction and enjoyment. If you are lucky enough to accomplish this feat, there will be an amplifier (or amplifiers) that will suit those speakers better than most others and there is fun to be had in finding those very components.
Only when those goals are achieved would I recommend attempting to add subwoofers.

No. Bandaid at best. Change either the speaker or amp. I use subs but run them full range so they have no effect on the amp or speaker.

The only place where "amplifier to speaker matching" would really be an issue in the bass would be with something like a single-ended triode with no global feedback and a resulting high output impedance, an OTL amplifier, or Bob Carver's "current source" outputs with a series resistance.

That has the side effect of increasing output where the speaker's impedance is high, like around the woofer and/or port resonances.

If you high-passed the main speakers+amplifier you'd get the port and perhaps woofer+box resonance out of the amplifier's pass-band which would reduce the problem.

You'd still have problems with reduced output were the impedance was low, like on .5 way speakers below the baffle step. Where that wasn't in the main speaker stop-band you'd still have problems.

Personally, I think that if you're going to use tone controls you should be honest about it and knowingly apply them before the power-amp in the shape tat best suits your room, placement, speaker defficiencies, and tastes.

That's more likely to be successful and cost less than trying multiple amplifier+speaker combinations hoping you'll be happy.

That all assumes you're not blowing rail fuses, sending the amplifier into thermal shutdown, or getting it to oscillate because it's unstable.

Where it's oscillating you want a better amplifier; and otherwise you may be better served with more efficient speakers.