I mean, how hard is it to look up Lendl's slam final results? People just don't do these things because it'll ruin their narrative...
Lost (to Borg)
Lost (to Connors)
Lost (to Connors)
Lost (to Wilander)
Won (French vs McEnroe)
Lost (to McEnroe)
Lost (to Wilander)
Now, imagine Lendl's back problems kicked in then (at 25, as was Murray), he had surgery, a year or two of searching for form with a marginally reduced game and then when he got a semblance of it back Wilander was dominating the tour and Borg had returned revitalised and, whilst not quite the same player, playing top 3 level tennis and both able to lolblock a still great but not quite as great Lendl?
Instead, Borg retired young, Wilander did have a dominant year, albeit in 1988 (and Wilander was hardly Novak), but then his career fell off a cliff, McEnroe was never the same after having kids and Connors was past it, meaning Lendl's next few slam finals were:
Won (USO vs McEnroe)
Won (FO vs Pernfors

)
Lost (to Becker)
Won (USO vs Mecir

)
After 11 slam finals he's only one better than Murray, having had one more slam final than Murray against a non legend.
Incidentally, Lendl played 3 slam finals against Boris and lost them all. He played one against Edberg who retired injured.
By the time Lendl finished competing in slam finals, in 1991, Sampras had won one slam (and would need another 3 years to make another final) and Agassi had yet to win any.
Even harder to look up Lendl's complete slam results and scorelines, hm? Besides 8 wins, Lendl suffered 23 GS losses to eventual winners (31 total); Murray 13 (16 total).
Lendl's wins:
Wilander in 3 + McEnroe in 5, Noah + Connors + McEnroe in 3, Pernfors et al. in 3 (Gomez in 4), Edberg + Mecir in 3, Wilander in 4, Wilander in 4 again, Noah in 4 + Mecir in 3, Edberg in RET.
Not all hard but beat prime Mac and Wilander for 4 of them, and didn't struggle against mugs otherwise when he won.
Lendl's losses to eventual winners:
McEnroe in 4, Borg in 5, Wilander in 5, Connors in 4, Noah in 4, McEnroe in 3, Connors in 4, Wilander in 3, McEnroe in 3, Wilander in 4, Edberg in 5, Becker in 3, Cash in 3, Wilander in 5, Chang in 5, Becker in 5, Becker in 4, Edberg in 3, Sampras in 5, Becker in 4, Edberg in 3, Edberg in 5, Sampras in 3.
8 five-setters, 7 four-setters though only the Becker ones highly competitive.
Murray's wins:
Djokovic in 5, Verdasco in 5 + Djokovic in 3, Tsonga in 5 + Raonic in 3.
The fact that Murray was on the brink against the legendary grasscourter (not) Verdasco puts a proper lid on his level there, notwithstanding the zombievic circus.
Murray's losses to eventual winners:
Nadal in 3, Federer in 3, Federer in 3, Nadal in 3, Djokovic in 3, Nadal in 3, Djokovic in 5, Federer in 4, Djokovic in 4, Nadal in 3, Djokovic in 4, Djokovic in 3, Djokovic in 4.
2012-13 only time he stayed competitive (Djo in 5, Fed in 4, Djo in 4, won two slams over Djo himself). Other than that, two sets taken in 10 such losses (AO 15 and RG 16), neither close.