Tatsumi should upscale quite a lot from 4.98 Tons since he one-shot the Earth dragon that preformed the feat. (It's also a chapter 1 feat, he has grown a lot since then)
Regarding skill, Tatsumi is very skilled, being completely aware of his surroundings and getting used to his opponents' fighting styles, analyzing them and adjusting properly allowing him to predict their next moves. (which would be useful against Muffet's danmaku, since a lot of her patterns can be predictable at times) and as a skilled assassin he should capable of sensing bloodlust/Killing intent (would be useful against Muffet's spiders since he can detect when they attacks.)
He is even capable of holding his own against people that are faster and more experienced than him like Akame and
Nyau for brief periods,
even landing a small hit on Zanku, who is
stronger than him and can read his mind.
And while Tatsumi usually relies on his stealth to give him an even bigger advantage that wouldn't be useful in a boxing ring, although he has already fought in a similar environment like the tournament he participated in where he managed to defeat skilled martial artists with no problem.
even if he could interact with them, her regular webs can’t be broken by someone who’s a whole one-shot above her.
Breaking from webs has to do with LS, not AP. If he can interact with the webs he should be able to break out of them, either via his Class M LS or via his sword. And are her strings really intangible? They aren't stated to be so, she was also shown to be capable of making real webs like the one she used to trap frisk and the profile doesn't give them intangibility (Although it does list them as spectral and she directly manipulates Frisk's SOUL making it purple so I guess they can be considered intangible with this information)
Also is there anything stopping Tatsumi from cutting Muffet's attacks since she uses actual physical things like donuts and spiders in her attacks and since monster magic in general can be used physically, like how Toriel uses fire magic to cook and even uses it to attack Flowey who doesn't have a SOUL (Also, only Sans has intangible attacks in his profile)
And I wouldn't exactly call Tatsumi completely inexperienced with danmaku since
he dodged this and
fought many people at once (yes he didn't do this in base but the skill and experience should also apply to his base form).