For shear simplicity and effectiveness...the Innokin Zenith is a hard one to beat...just so easy to set up and use. The coils are pretty long lived, rediculously easy to change over (just spin ff the bottom retainer, pull out old coil, push in new one, and spin retainer back on) & best of all, it's a top filler too. The Zenith is here in the UK as a TPD 2ml, but i bought the 4ml version from Le Petite Vapotuer,
https://www.lepetitvapoteur.com/en/clearomisers/4532-zenith-clearomiser-innokin.html. Service is excellent, and if you chuck in a couple packs of coils in, to take the cost to around 30 Euros, and you get free fast delivery too. I also got cute freebies with delivery! Coils available are 1.6, 0.8 & the 0.5 Plex.
As you're a MTL vaper, i recommend the 1.6 ohm coils, which is what i use....they're bulletproof. I can often get several weeks out of one, if i don't cane it. The only issue you might have with the Zenith, is it's size. The Zlide is 22mm, the Zenith is 24.7mm, and i think the Arc 5 is only about 20mm wide, so there would be a overlap alas.
But if you get bigger battery mod sometime (most vapers have more than one....i have loads!)..then defo try the Zenith out sometime...it's a nice performer.
As for the harshness, you're experince, that could down to the nicotine strenght. Most newbies (including myself when i started last year)...will need to play around with the different ratios, flavours and nic strenghts, until you find something that works for you.
Incidentally, the Zenith works comfortably with thicker juices upto 70VG max...but i use 50/50 myself.
One other tank you could try, is Aspire Nautilus....either the original 5ml, the 2ml narrow Mini, or 2S. Along with the Zenith...i would say these these are still pretty unbeatable in terms of performance. I started with the Nauty 2, then got a 2ml Mini..and now i use an original 5ml, imported from China. That one is still my daily user. The only negatives i would say against the Aspire BVC coils, is the durability, which can be a little fickle at times, depending on whether you get a duff pack or not. But for performance the old fashioned Nautilus original is still the MTL daddy imo.
So...as you're a newbie..i'll stick to recommending the Zenith..when you've got a bigger mod for it!