I find familysearch is much better at finding variations of names than Scotlandspeople.
You have to use wildcards on Scotland's People to pick up all the variations.
In FS you get variations if someone, somewhere, has flagged them as known variations and instructed the program to return them together, or if they are a Soundex match or something like that. But if no-one has told the program that a certain weird-looking name is a spelling variant of another, it won't necessarily find it.
FamilySearch does tend to return too many variations, some of them implausible. However it's the omissions that I would worry about. For example, for a long time it would not return M*c xxxx (with a space) if you searched for M*cxxxx.
Also, FS has quite good coverage of the Old Parish Registers in the northern parts of Scotland, but not the southern parts. And some registers are simply missing, for example they forgot to index the baptisms in the parish of Duffus between 1820 and 1854. In other cases they indexed all the male baptisms but not the female ones, or vice versa.
And sometimes it produces very odd results, like missing a baptism or birth if you put in the mother's surname or the child's middle name, but finding it if you take those bits of information out of your search parameters, even though the spelling is identical and it is in the indexed listing.
So although FS may find some (even many) name variations, it can't be relied on to contain all the available information, or to find everything that it contains when you search it. It's an
extremely useful search aid, but it's not 100% reliable.
(And I won't start about the 'submitted' listings on FS, some of which are pure fantasy.)