At least some of the material she can't sing even now - her version of Deep Silent Complete is completely off, as far as vibe and atmosphere go, so is Ever Dream. I could also live without the shrieking chorus of She Is My Sin in Floor's delivery. Sounds like Christina Aguillera more than anything to me, sorry.
That's not necessarily her fault, the songs are written in some way, but just because Floor is technical doesn't mean she fits or that she would be a better singer in the future. Bruce at least had most of the songs written for him, it would be Blaze who would be the outlier - if they didn't decide to go the X Factor route and make a lot of music that would fit Blaze like a glove.
(also, if you want to mention Stargazers - the live version with Floor is at least several steps lower so that she could sing it comfortably, and the song sounds darker, drearier, more boring as a result. But I digress)
But comparing it with Di'Anno is just ridiculous. Floor sounds far better singing some of the material and way worse singing some of the rest. I can't imagine Di'Anno sounding better singing anything, his era or not.
To be more abstract, I really appreciate that Tuomas has managed to write at least some songs for all three of the very diverse singers that actually build on their strengths and the charm and appeal of these songs could not be (or would not be) ever quite recaptured by the others – let’s see, at least one such as an example:
Sacrament for Tarja (apart from the above that I mentioned)
Amaranth for Anette
Weak Fantasy for Floor - although I hate it for other reasons, it comes to mind first as a song that couldn’t be recaptured by any of the other two singeresses, especially the breathy rasp in the verse.
I know we were talking about Tarja, but, like, for example, Amaranth really requires this light, breathy, fairiesque, acrobatic voice that does the jovial and whimsical jumps in the chorus - in the words of my wife, who is as impartial as it could be (she isn't particularly enamoured by Nightwish in general and doesn't have a preference for any of the vocalists) - "it sounds like replacing a butterfly with a bulldozer."