No offense is intended. My understanding was that this sniff is licensed under the LGPL3 though, which I understood would permit copying and modifying as required. In any case, I do not intend to upset or offend.

IANAL, but as far as I understand it, forking and updating (while retaining the original commits and copyright) is okay. Copying, adjusting and then passing it off as your own, is not.

The Slevomat sniff is absoltuely massive and has a number of bloated dependencies that we are keen to avoid. This is not a set and forget situation for us as our community has hundreds of plugins that need to be updated in the same way.

Could you elaborate on that ? I mean: the Slevomat sniff collection is large, true, but you would only be using one sniff of it in this case.
As for dependencies, they only have three - two of which overlap with PHPCompatibility:

	"require": {
		"php": "^7.2 || ^8.0",
		"dealerdirect/phpcodesniffer-composer-installer": "^0.6.2 || ^0.7 || ^1.0",
		"phpstan/phpdoc-parser": "^1.23.1",
		"squizlabs/php_codesniffer": "^3.9.0"
	},

So, you're only really talking about the phpstan/phpdoc-parser dependency and that dependency has no underlying dependencies either.