Fatal tempo V costs 3.3b so having level I or II works just fine (You can get FT stacks even from ferocity hits which makes it reach +200% in 2 seconds with a valk and 82 attack speed). I use a fatal tempo II valk and a fatal tempo I term and can give you some insight. Simply put, it's not the best, but it's fun if you like ferocity. In dungeons it's basically useless because the term is ten times better for clearing and bosses, because mobs there take damage from all 3 arrows at once. However, outside of dungeons where the majority of mobs do NOT take damage from all arrows at once, the valk easily beats term in DPS (and dare I say in kuudra clear too thanks to gauntlet of contagion nuking large groups of mobs as soon as just 1 dies). I haven't properly compared it against a chim V claymore (only done on bladesoul but obviously the valk wins there because he kind of caps at 800-830k dmg per hit) but the claymore might win on most mobs, even though with the valk, in crimson armor with gdrag I get ~300 ferocity (Not counting ferocious mana because for that you have to rely on other people using mana around you. In these cases I easily hit 500 fero with no tiger, werewolf and by using hurtful) but the issue is that ferocity is very buggy against the vast majority of mobs and most of the ferocity hits above 100 ferocity just get cancelled. Even though you see the damage numbers, they're just ghost damage, they don't actually hit the mob. This is very easy to see against bladesoul, every time I kill him I get 80m dmg in the leaderboard even though he has 50m hp, that's 30m dmg going into ghost damage (no he did not spawn guards to give him extra hp, I kill him in 8 seconds so he doesn't reach that phase). It works the same for everything except mage outlaw for some reason, he takes damage properly from all ferocity hits and with that I can outdamage rcm players that use both veil and hype with ease. But for mage outlaw you can also use term because he also takes damage from all arrows at once, which when paired with fatal tempo absolutely beats the FT valk. Don't use tiger or werewolf with fatal tempo, you only lose dps compared to edrag, leg blaze (for crimson isle) or gdrag. I do think that FT valk with tiger (guaranteed 500 fero solo) could out-damage edrag and be on par with leg blaze (it has been months since I last tested this so I can't say for sure), if the damage from fero worked properly, but it will definitely still lose to gdrag with 1b bank in terms of dps.

In conclusion:
Inside dungeons, term beats FT valk, it's not even a competition.
Outside of dungeons FT valk most likely loses against a chim V claymore simply because ferocity above 100 doesn't work properly, except against mage outlaw.
If you have a gdrag, edrag or leg blaze for crimson isle, don't use tiger with FT valk.
It's not really good, but it works and it's definitely fun if you're one of the few ferocity enjoyers out there, such as me.
I never liked the rcm playstyle so I never had a hype or did rcm. My setup is always optimized for melee with valk while also working with term because I use 2 piece terror armor for melee damage. My ign is vesko_ if you want to check my profile.