4* servant that is better than 5* servant?

For specific teams even 2 star servants can outshine some 5 stars

But the tier lists on this site cover general utility quite well.

For example, I'm pretty sure only 2 4 stars come close to the first 2 tiers of 5 star servants here. Those two being Heracles and Mash.

The servants outside the top 2 tiers of the 5 star tier list are all also amazing but have intrinsic flaws that make them either limited to certain teams or just overall stat sticks. Even with all that said, only the tier 1 of the 4 star list can really provide enough versatility to outperform those lower tier 5 stars.

So yea, Herc and Mash. Personally I've grailed my herc as I feel he is that good. Another prominent example of where I use a 4 star over a 5 star is I much prefer using kintoki Rider over Broskandar.

Links to the tier lists:
https://grandorder.gamepress.gg/4-star-tier-list
https://grandorder.gamepress.gg/5-star-tier-list

Not all SSRs are created equal. Look at Medb. She is pretty terrible. I’d take pretty much any of the 4*s over her. Salter is only a slightly weaker version of OG Saber with a cheaper cost.

A lot of people like Herc as an SR Beserker cause of his serviceability over some 5*s. Li Shuwen can out damage 5* lancers in an Arts team. There are examples in each class where servants with the right kits or NPs just fit into rolls better than SSRs. That being said, there is still a reason they are 5*s and a lot of the time will be more powerful when you can put them in the right roll.

But plenty of people here will tell you Cu is their best Lancer even as a 3*. I don’t particularly agree, he’s definitely the best 3* in the game, but I won’t say he’s the best Lancer lol.

Again, it all depends on the enemy and such, unlike some other game, every servant has a scenario where it shines. So there is no straight answer to that. It's more important to understand the characteristic of each servant and utilize them as they are intended.
However, if you are just beginning, you are probably looking for some servants that can help you farm or go through the main story line. Usually you will be looking at berserker since they can hit everyone effectively. Lancelot is a good one for farming although his NP rate sucks, so you will need a nice CE or someone to help his NP. Heracles is probably the best surviving berserker that can help you through a lot of high difficulty quest. However, both of these has a SSR that sort of replace them.
Technically, a lot of the welfare servants, which are 4 stars, are better than 5 stars since they will always be NP lv.5, but that's another story.

Depends on which 5* we're talking about. Some, like Waver, will always be better than any 4* you could find (assuming a fair comparison). Others, like Medb are typically worse than a lot of 4* servants. Good 4*s in general are:
- Herc (High durability with berserker buster attacks)
- Rider Kintoki (immensely well-synergised quick-based kit, great damage/NP charge, NP5)
- Chloe (NP spamming, NP5)

There's a very broad answer to this just because SRs can always be as good as SSRs dependent on the situation (SRs might have better skills in several battle scenarios) while also having a very close stat gap (some max-fou'd SRs are VERY close in stats to SSRs).

Here's a few SSRs that are outclassed by SR alternatives (considering certain scenarios are present)

1. (Waver)

-----Nitocris: beats Waver in raw-damage over the course of the battle thanks to her NP. She works better as an independent unit and can solo nodes while waver is support-specific and requires a team to do well.

-----Medea (lily): Better at keeping your party alive thanks to 2 on-demand heals and 2 debuff removals. Although Waver does this with his 2nd skill and NP which mitigates damage that would otherwise cause the need for healing in the first place, Medea ensures that your whole party remains on the field after the fact. (she works well with Jeanne and arts servants in a stall comp)

-----Irisviel: Same function as Medea but is used in riskier situations as her NP's guts acts as a safety net for more difficult fights where you can ensure 2 or more bursts from your main frontline damage dealers. before they're taken out. She will continue to support heavy damage dealers in the backline to finish off bosses.

----------Medea and Iri work EXTREMELY well with Rama, Nero, Marie, David, and Ushi thanks to their utility and guts/evade skills. This means they will do a respectable amount of damage while alive also being extremely difficult to kill (surpassing Cu's survivability).

2. (MHX)

-----Every single SR archer: Yes, MHX has an anti saber skill in her kit but she's an assassin and any archer can do her job more efficiently at destroying sabers.

-----Emiya Assassin: definitely less gimmicky lower cooldown skills

-----Carmilla: definitely less gimmicky lower cooldown skills and better team support (amazing debuffer, female nuker, and NP spammer)

3. (Mordred/Altria/Saber Shiki)

-----Rama & Lancelot: Identical stats to SSR sabers (once fou'd) and good skillsets alongside that. Rama easily outdamages SSR sabers due to his passive (putting his non-fou'd max atk over 10k surpassing Saber Shiki's/Altria's max once fou'd at 11k). Rama works better in crit teams/demonic slaying comps over Altria, Mord, and Shiki just because of his 1st active skill & NP. He also does better single-target damage which is more viable in boss fights.

4. (Davinci)

-----Every SR support-specific caster (helena, liz, etc... even hans): Davinci has a greedy kit providing no team support whatsoever while Helena and Hans can provide SSR-grade aid for the team.

5: (Cu Alt)

-----Herc: Although Cu does far more damage than him, Herc has far better staying power with (lv10 bond CE, 3rd/2nd skill) and can be an efficient berserker for stalling AND dealing a good amount of damage.

-----Cu: You know exactly why

6. (Medb)

-----Out-damaged by a lot of fou'd SRs and 3 star servants: An NP5 Robin, Ushi, or Euryale can outdamage her and Medb is really only powerful inside her niche.

-----Sakata Kintoki: Think of Francis Drake but rides a motorcycle and is slightly less powerful.

-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-

After typing for more than an hour, I've come to realize that there are too many variables that affect this list and should've stuck with my initial statement. This list can go on for EVERY SSR in the game as there are an infinite amount of scenarios in which a SR can/will do better than an SSR (Team comps, RNG, Fou'd stats, Skill sets, Skill level, Enemies involved, class inclination, soloing nodes vs having a team, enemy-type modifiers, etc).

Heck a Cu can solo hands while a Waver can't.